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.math.RoundingMode;
import java.text.DecimalFormat;
import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.net.ssl.SSLContext;

public class Main
{  
   static long mod=(long)(998244353);
   static int[] sieve;
   static ArrayList<Integer> primes;
   
   public static void main(String[] args) throws java.lang.Exception
   {	  	
	     fast s = new fast();
	     PrintWriter out=new PrintWriter(System.out);
	     Scanner sc=new Scanner(System.in);
	     StringBuilder fans = new StringBuilder();

	     int k=s.nextInt();
	     int xx=k;
	     
	     String str=s.nextLine();
	     
	     if(k==0) k=2;
	     
	     int prev[]=new int[1000005];
	     int next[]=new int[1000005];
	     
	     int i=0;
	     
	     int n=str.length();
	     
	     int pre=0;
	     int nxt=0;
	     int kk=0;
	     
	     int first=-1;
	     int cc=0;
	     
	     for(i=0;i<n;i++) if(str.charAt(i)=='1') cc++;
	     
	     for(i=0;i<n;i++) if(str.charAt(i)=='1') {prev[i]=-1;pre=i;first=i;break;}
	     for(kk=n-1;kk>=0;kk--) if(str.charAt(kk)=='1') {next[kk]=n; break;}
	     i++;
	     while(i<n)
	    	 {
	    		if(str.charAt(i)=='1')
	    			{
	    				next[pre]=i;
	    				prev[i]=pre;
	    				pre=i;
	    			}
	    		i++;
	    	 }
	     
	     int count=1;int j=first+1;
	     
	     for(;j<n && count<k;j++)
	    	 {
	    		 if(str.charAt(j)=='1') count++;
	    	 }
	     
	     int mm=first; int nn=j-1;
	     
	     long ans=0;
	     long temp3=0;
	     
	     if(count<k && xx>=1) {System.out.println("0"); return;}
	     
	     long ans1=0;
	     ans1+=(n-1-kk)*(n-kk)/2;
	     ans1+=(first*(first+1))/2;
	     
	     while(nn<n && first!=-1 && first!=kk)
	    	 {
	    		 int temp1=next[nn]-nn;
	    		 int temp2=mm-prev[mm];
	    		 
	    		 int temp4=Math.max(0,nn-mm-1);
	    		 
	    		 temp3+=(temp4*(temp4+1))/2;
	    		 
	    		 ans+=(long)temp1*temp2;
	    		 
	    		 mm=next[mm];
	    		 nn=next[nn];	 
	    	 }
	     if(xx==0 && cc==1)
	    	 {
	    		 long tt=((long)first*(first+1))/2;
	    		 long ttt=((long)(n-1-first)*(n-first))/2;
	    		 System.out.println(tt+ttt);
	    	 }
	     else if(xx==0 && first==-1) System.out.println(((long)n*(n+1))/2);
	     else if(xx==0) System.out.println((long)ans1+temp3);
	     else if(xx==1 && cc==1) System.out.println(ans1+1);
	     else System.out.println((long)ans);
   }
   
   
static class fast {   
	private InputStream i;
		private byte[]  buf = new byte[1024];
		private int curChar;
		private int numChars;
		
		//Return floor log2n
		public static int log2(int bits) // returns 0 for bits=0
			{
			    int log = 0;
			    if( ( bits & 0xffff0000 ) != 0 ) { bits >>>= 16; log = 16; }
			    if( bits >= 256 ) { bits >>>= 8; log += 8; }
			    if( bits >= 16  ) { bits >>>= 4; log += 4; }
			    if( bits >= 4   ) { bits >>>= 2; log += 2; }
			    return log + ( bits >>> 1 );
			}
		
		public static boolean next_permutation(int a[])
		   {
			   int i=0,j=0;int index=-1;	   
			   int n=a.length;
			   
			   for(i=0;i<n-1;i++)
				   if(a[i]<a[i+1]) index=i;
			   
			   if(index==-1) return false;
			   i=index;

			  
			   for(j=i+1;j<n && a[i]<a[j];j++);

			   int temp=a[i];
			   a[i]=a[j-1];
			   a[j-1]=temp;
			   	   
			   for(int p=i+1,q=n-1;p<q;p++,q--)
			   {
				   temp=a[p];
				   a[p]=a[q];
				   a[q]=temp;
			   }
			   
			   return true;
		   }
		   
		   
		public static void division(char ch[],int divisor)
		   {
			   int div=Character.getNumericValue(ch[0]); int mul=10;int remainder=0;
			   StringBuilder quotient=new StringBuilder("");
			   for(int i=1;i<ch.length;i++)
			   {
				   div=div*mul+Character.getNumericValue(ch[i]);	
				   if(div<divisor) {quotient.append("0");continue;}
				   quotient.append(div/divisor);
				   div=div%divisor;mul=10;
				   
			   } 
			   remainder=div;
			   while(quotient.charAt(0)=='0')quotient.deleteCharAt(0);	   
			   System.out.println(quotient+" "+remainder);	  
		   }
		
		public static void sieve(int size)
		{
			sieve=new int[size+1];
			
			primes=new ArrayList<Integer>();
			
			sieve[1]=1;
			
			for(int i=2;i<=Math.sqrt(size);i++)
			{
				if(sieve[i]==0)
				 {
					for(int j=i*i;j<size;j+=i) {sieve[j]=1;}
				 }
			}
			
			for(int i=2;i<=size;i++)
			{
				if(sieve[i]==0) primes.add(i);
			}
		}
		
		public static long pow(long n, long b, long MOD)
		   {
		       long x=1;long y=n; 
		       while(b > 0)
		       {
		           if(b%2 == 1)
		           {
		               x=x*y;
		               if(x>MOD) x=x%(MOD);
		           }
		           y = y*y;
		           if(y>MOD) y=y%(MOD); 
		           b >>= 1;
		       }
		       return x;
		   }


		public static long mod_inv(long n,long mod)
		{
			return pow(n,mod-2,mod);
		}
		
		 public static int upper(Integer[] a,int start,int end,int key)
		 {
			   int mid=(start+end)>>1;
			   if(start==end && a[mid]<key) {return -1;}
			   if(start>end) return -1;

			   if(a[mid]>=key && (((mid-1)>=0 && a[mid-1]<key) || (mid-1)==0)) return mid;
			   else if(a[mid]== key && (mid-1)>=0 && a[mid-1]==key) return upper(a,start,mid-1,key);   
			   else if(key>a[mid]) return upper(a,mid+1,end,key);
			   else return upper(a,start,mid-1,key);
		}
		 
		 public static int lower(int[] a,int start,int end,int key)
		 {
			   int mid=(start+end)>>1;
			   if(start==end && a[mid]>key) {return -1;}
			   if(start>end) return -1;

			   if(a[mid]<=key && (((mid+1)<a.length && a[mid+1]>key) || (mid+1)==a.length)) return mid;
			   else if(a[mid]== key && (mid+1)<a.length && a[mid+1]==key) return lower(a,mid+1,end,key);   
			   else if(key>=a[mid]) return lower(a,mid+1,end,key);
			   else return lower(a,start,mid-1,key);
		} 
		   
		public long gcd(long r,long ans)
		{
			if(r==0) return ans;
			return gcd(ans%r,r);
		}
		public fast() {
			this(System.in);
		}
		public fast(InputStream is) {
			i = is;
		}
		public int read() {
			if (numChars == -1)
				throw new InputMismatchException();
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = i.read(buf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (numChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}
		public String nextLine() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isEndOfLine(c));
			return res.toString();
		}
		public String nextString() {
     		int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isSpaceChar(c));
			return res.toString();
		}
		public long nextLong() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			long res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			} while (!isSpaceChar(c));
			return res * sgn;
		}
		public int nextInt() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			int res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			} while (!isSpaceChar(c));
			return res * sgn;
		}
		public boolean isSpaceChar(int c) {
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}
		public boolean isEndOfLine(int c) {
			return c == '\n' || c == '\r' || c == -1;
		}

	}	
}