A string is binary, if it consists only of characters "0" and "1".

String v is a substring of string w if it has a non-zero length and can be read starting from some position in string w. For example, string "010" has six substrings: "0", "1", "0", "01", "10", "010". Two substrings are considered different if their positions of occurrence are different. So, if some string occurs multiple times, we should consider it the number of times it occurs.

You are given a binary string s. Your task is to find the number of its substrings, containing exactly k characters "1".

Input

The first line contains the single integer k (0 ≤ k ≤ 106). The second line contains a non-empty binary string s. The length of s does not exceed 106 characters.

Output

Print the single number — the number of substrings of the given string, containing exactly k characters "1".

Please do not use the %lld specifier to read or write 64-bit integers in С++. It is preferred to use the cin, cout streams or the %I64d specifier.

Examples

Input

1
1010


Output

6


Input

2
01010


Output

4


Input

100
01010


Output

0

Note

In the first sample the sought substrings are: "1", "1", "10", "01", "10", "010".

In the second sample the sought substrings are: "101", "0101", "1010", "01010".


        import java.io.*;


         
            import java.math.BigInteger;
        import java.text.DecimalFormat;
        import java.util.*;

        
        
             public class Main {
            	public static InputReader in;
                public static PrintWriter pw;
             
             
             
            	public static void main(String args[]) 
            	{
            		new Thread(null, new Runnable() {
                        public void run() {
                            try{
                                solve();
                            }
                            catch(Exception e){
                                e.printStackTrace();
                            }
                        }
                    }, "1", 1 << 26).start();
                }
            	static ArrayList<Integer> g[];
            	static ArrayList<Integer> h[];
            	static boolean visited[];
            	static int[] parent;
            	static int par[];
            	static int degree[];
            	static int edjes=0;
            	static int start=-1;
            	static int end=-1;
            	static int Total=0;
            	static int time1[];
            	static int time2[];
            	static int glob=0;
            	static int[] ans;
            	static boolean vis2[][];
            	//static long sum1=0;
            	//static long val[];
                static ArrayList<Integer> levels[];
                static int max=0;
                static int lev=1;
                static ArrayList<Integer> nodes[];
                static ArrayList<Integer> values[];
                static int depth[];
                static boolean found=false;
               // static long sm[];
                static int sum1=0;
                static int pre[][];
                static int subtree[];
               static  int cnt=0;
               static  HashMap<String,Integer> hm;
               static int sm[];
               static int size[];
               static long mul[];
               static long d[]=new long[1000000];
               static int tot=0;
               static long highest=(long)1e9;
               static boolean bit=false;
                static Stack<Integer> tt=new Stack();
               static HashSet<Character> set;
         	   static long fact[],num[];
         	   static long MOD=1000000007;
         	   static int value[];static int premen[];
         	   static int count=0,index=0;
         	   static double ans11[];
         	   static int price[];
         	   static ArrayList<String> hp[][];
         	   static boolean visit[][];
         	   static int cnu[]=new int[1000001];
         	   static int label=1;
         	   static int his[][];
         	   static int size1=0;
         	   static int up[],down[];
         	   static int TotalUp=0;
         	   static long dist[];
         	//   static HashMap<String,Integer> hm1=new HashMap();
         	  // static HashMap<Integer,Integer> hm2=new HashMap();
         	   static TreeSet<Long> set1=new TreeSet();
         	  static  long DP[][][]=new long[20][200][1500];
         	 	static int t=-1,n=-1;
         	 	static int two[],min[],r[];
         	 	static int total[];static int black[];
         	 	static int Parent[];
         	 	static int max2[];
         	// 	static int tin[],tout[],a[];
         	 public static void solve() throws FileNotFoundException{
            		
            	
            		 in = new InputReader(System.in);
            		 pw = new PrintWriter(System.out);  
            	/*	 String p=in.readString();
            	     char c[]=p.toCharArray();
            	     int z[]=new int[p.length()];
            	     z[0]=0;
            	     int left=0;
            	     int right=0;
            	     for(int i=1;i<p.length();i++)
            	     {
            	    	 if(i>right)
            	    	 {
            	    		 
            	    		 left=right=i;
            	    		 while(right<p.length()&&c[right]==c[right-left])
            	    			 right++;
            	    		 z[i]=right-left;
            	    		 right--;
            	    	 }
            	    	 else
            	    	 {
            	    		 int k=i-left;
            	    		 if(z[k]<right-i+1)
            	    		 {
            	    			 z[i]=z[k];
            	    		 }
            	    		 else
            	    		 {
            	    			 left=i;
            	    			 while(right<p.length()&&c[right]==c[right-left])
                	    			 right++;
                	    		 z[i]=right-left;
                	    		 right--;
            	    		 }
            	    	 }
            	    	  
            	     }*/
            		 int k=in.nextInt();
            		 String s=in.readString();
            		 int pre[]=new int[s.length()];
            		 
            		 if(k==0)
            		 {
            			 long tmp=0;
            			 long co=0;
            			 for(int i=0;i<s.length();i++)
            			 {
            			if(s.charAt(i)=='0')
            			{
            				co++;
            			}
            			else 
            			{
            				tmp+=((co)*(co+1)/2);
            				co=0;
            			}
            			 }
            			 if(co>0)
            			 {
            				 tmp+=((co)*(co+1)/2);; 
            			 }
            			 System.out.println(tmp);
            			 return;
            		 }
            		long dp[]=new long[s.length()+1];
		    		
		    		dp[0] = 1;
		    		
		    		long ans = 0;
		    		
		    		long sum = 0;
		    		
		    		for(int i = 0;i<s.length();i++){
		    			if(s.charAt(i) == '1'){
		    				sum++;
		    				
		    			}
		    			
		    			if(sum >= k)
		    				ans += dp[(int) (sum - k)];
		    				
		    				dp[(int) sum]++;
		    		}
		    		System.out.println(ans);
         	 }
         	 public static boolean check(int a[][],int b[][],int n,int m)
         	 {
         		for(int k=0;k<n;k++)
    			{
    				for(int l=0;l<m;l++)
    				{
    					if(a[k][l]!=b[k][l])
    					{
    						return false;
    						//break;
    					}
    				}
    			}
         		return true;
         	 }
        
            
          		public static void bfs(int x)
         	 {
         		 visited[x]=true;
         		 Queue<Integer> Q=new LinkedList<Integer>();
         		 Q.add(x);
         		 while(!Q.isEmpty())
         		 {
         			 int count=Q.size();
         			 while(count>0)
         			 {
         				 int p=Q.poll();
         				 visited[p]=true;
         				 for(int y:g[p])
         				 {
         					 if(!visited[y])
         					 {
         						 Q.add(y);
         					 }
         				 }
         				 count--;
         			 }
         		 }
         	 }
         	 public static void depth(int curr,int parent)
         	 {
         		 visited[curr]=true;
         		 for(int x:g[curr])
         		 {
         			 if(!visited[x])
         			 {
         				 depth[x]=depth[curr]+1;
         				 depth(x,curr);
         			 }
         		 }
         	 }
         	
         	 static int Par[]=new int[202];
         	 public static void Height(int cur,int par){
         		 Par[cur]=par;
         		 visited[cur]=true;
         		 int t=0;
         		 for(int x:g[cur])
         		 {
         			 if(!visited[x])
         			 { 
         				 t++;
         				 Height(x,cur);
         				 high[cur]=Math.max(high[cur], high[x]+1);
         			 }
         		 }
         		 if(t==0)
         		 {
         			 high[cur]=0;
         		 }
         	
         	 }
         	 static int dia[]=new int[202];
         	 static int high[]=new int[292];
         	 public static void Diameter(int curr,int parent)
         	 {
         		visited[curr]=true;
         		int trees=0;
         		ArrayList<Integer> set=new ArrayList();
         	
         		for(int x:g[curr])
         		{
         			if(!visited[x])
         			{
         				trees++;
         				Diameter(x,curr);
         				dia[curr]=Math.max(dia[curr],high[x]);
         				set.add(high[x]);
         			}
         		}
         		if(set.size()>=2)
         		{
         			Collections.sort(set,Collections.reverseOrder());
         			dia[curr]=Math.max(dia[curr],set.get(0)+set.get(1)+2);
         		}
         		else if(set.size()>0)
         		{
         			dia[curr]=Math.max(dia[curr],set.get(0)+1);
         		}
         		if(trees==0)
         		{
         			dia[curr]=0;
         		}
         
         	 }
         	 
              	 
         	 public static boolean IsPal(String s)
         	 {
         		 char c[]=s.toCharArray();
         		 for(int i=0;i<c.length/2;i++)
         		 {
         			 if(c[i]!=c[s.length()-1-i])
         				 return false;
         		 }
         		 return true;
         	 }
         	public static void Merge(long[] a,int p,int r){
                if(p<r){
                    int q = (p+r)/2;
                    Merge(a,p,q);
                    Merge(a,q+1,r);
                    Merge_Array(a,p,q,r);
                }
            }
            public static void Merge_Array(long a[],int p,int q,int r){
               long b[] = new long[q-p+1];
                long c[] = new long[r-q];
                for(int i=0;i<b.length;i++)
                    b[i] = a[p+i];
                for(int i=0;i<c.length;i++)
                    c[i] = a[q+i+1];
                int i = 0,j = 0;
                for(int k=p;k<=r;k++){
                    if(i==b.length){
                        a[k] = c[j];
                        j++;
                    }
                    else if(j==c.length){
                        a[k] = b[i];
                        i++;
                    }
                    else if(b[i]<c[j]){
                        a[k] = b[i];
                        i++;
                    }
                    else{
                        a[k] = c[j];
                        j++;
                    }
                }
            }
         	 
         	 
         	 
         	
         	
               
         	  public static void dfs1(int curr,int parent)
         	  {
         		  visited[curr]=true;
         		  
         		  for(int x:g[curr])
         		  {
         			  
         			  if(x==parent)continue;
         			  depth[x]=depth[curr]+1;
         			  up[x]=up[curr];
         			  if(h[x].contains(curr)){
         				  up[x]++;
         				  TotalUp++;
         			  }
         			  dfs1(x,curr);
         		  }
         	  }
         	 
                
                
                public static void dfs(int curr,int Parent)
                {
                	visited[curr]=true;
                	size[curr]=1;
                	parent[curr]=Parent;
                	count++;
                	if(value[curr]>0)
                	{
                		index=value[curr];
                	}
                	for(int x:g[curr])
                	{
                		if(!visited[x])
                		{
                			dfs(x,curr);
                			size[curr]+=size[x];
                		}
                	}
                }
                static long ncr(long a, long b){
        			if(b>a || b<0) return 0;
        			long f = (fact[(int) a]*modInverse(((fact[(int) b]*fact[(int) (a-b)])%MOD), MOD))%MOD;
        			return f;
        		}
        		static long modInverse(long a, long mOD2){
                    return  power(a, mOD2-2, mOD2);
        }
        static long power(long x, long y, long m)
        {
            if (y == 0)
                return 1;
            long p = power(x, y/2, m) % m;
            p = (p * p) % m;
         
            return (y%2 == 0)? p : (x * p) % m;
        }
         
                public static long gcd(long x, long y) {
            		if (x == 0)
            			return y;
            		else
            			return gcd( y % x,x);
            	}	
                public static long power(long a,long b)
        		{
        			long result=1;
        			while(b>0)
        			{
        				if(b%2==1)
        					result*=a;
        				a=a*a;
        				b/=2;
        			}
        			return result;
        		}
                static class Pair implements Comparable<Pair>{
                	    int l;int r;
                		Pair(int val,int index){
                	     	this.l=val;
                			this.r=index;
                			
                		}
                		@Override
                		public int compareTo(Pair o) {
                                
                                	return r-o.r;
                		}
                				
                	}
            	static class InputReader {
             
            		private InputStream stream;
            		private byte[] buf = new byte[8192];
            		private int curChar, snumChars;
            		private SpaceCharFilter filter;
             
            		public InputReader(InputStream stream) {
            			this.stream = stream;
            		}
             
            		public int snext() {
            			if (snumChars == -1)
            				throw new InputMismatchException();
            			if (curChar >= snumChars) {
            				curChar = 0;
            				try {
            					snumChars = stream.read(buf);
            				} catch (IOException e) {
            					throw new InputMismatchException();
            				}
            				if (snumChars <= 0)
            					return -1;
            			}
            			return buf[curChar++];
            		}
             
            		public   int nextInt() {
            			int c = snext();
            			while (isSpaceChar(c))
            				c = snext();
            			int sgn = 1;
            			if (c == '-') {
            				sgn = -1;
            				c = snext();
            			}
            			int res = 0;
            			do {
            				if (c < '0' || c > '9')
            					throw new InputMismatchException();
            				res *= 10;
            				res += c - '0';
            				c = snext();
            			} while (!isSpaceChar(c));
            			return res * sgn;
            		}
             
            		public long nextLong() {
            			int c = snext();
            			while (isSpaceChar(c))
            				c = snext();
            			int sgn = 1;
            			if (c == '-') {
            				sgn = -1;
            				c = snext();
            			}
            			long res = 0;
            			do {
            				if (c < '0' || c > '9')
            					throw new InputMismatchException();
            				res *= 10;
            				res += c - '0';
            				c = snext();
            			} while (!isSpaceChar(c));
            			return res * sgn;
            		}
             
            		public int[] nextIntArray(int n) {
            			int a[] = new int[n];
            			for (int i = 0; i < n; i++)
            				a[i] = nextInt();
            			return a;
            		}
             
            		public String readString() {
            			int c = snext();
            			while (isSpaceChar(c))
            				c = snext();
            			StringBuilder res = new StringBuilder();
            			do {
            				res.appendCodePoint(c);
            				c = snext();
            			} while (!isSpaceChar(c));
            			return res.toString();
            		}
             
            		public boolean isSpaceChar(int c) {
            			if (filter != null)
            				return filter.isSpaceChar(c);
            			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
            		}
             
            		public interface SpaceCharFilter {
            			public boolean isSpaceChar(int ch);
            		}
            	}
            }
          
     

