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".
// This problem is similar to finding number of subarrays with sum equal to given sum
import java.io.*;
import java.util.*;
public class Solution{ 

           static long findSubarraySum(int arr[], int n, int sum)  {  
       
        HashMap <Integer,Long> prevSum = new HashMap<>();  
        
        long res = 0;  
        
        int currsum = 0;  
        
        for (int i = 0; i < n; i++) {  
         
            currsum += arr[i];  
              if (currsum == sum)   
                  res++;          
        
              if (prevSum.containsKey(currsum - sum))   
                   res += prevSum.get(currsum - sum);  
              
            Long count = prevSum.get(currsum); 
            if (count == null) 
                prevSum.put(currsum, 1l); 
            else
                prevSum.put(currsum, count+1);  
        }  
        
        return res;  
    } 
                

                 public static void main(String[] args){

                       int k = intt();      
                       char s[] = (str()).toCharArray();
                       int n = s.length;
                       int sum[] = new int[n];
                       for(int i=0;i<n;i++) if(s[i]=='1') sum[i]=1;
                   
                              System.out.println(findSubarraySum(sum,n,k)); 

                 
              }
                static FastReader sc=new FastReader();
                static PrintWriter out = new PrintWriter(System.out);
                static int mod=1000000007;

                static int intt(){
                       int x = sc.nextInt();
                       return(x);
                }
               static long longg(){
                          long x = sc.nextLong();
                           return(x);
                }
               static double doublee(){
                          double t = sc.nextDouble();
                           return(t);
                }
              static String str(){
                       String s = sc.next();
                         return(s);
                }
              static String strln(){

                        String s = sc.nextLine();
                           return(s);
              }
              static long pow(long a,long b){
                       long ans=1;
                      while(b>0){
                          if(b%2==1)
                              ans=(ans*a);
                              a=(a*a)%mod;
                              b=b/2;
                      }
                    return(ans);
                }
             static long GCD(long a,long b){
                           if(b%a==0)
                               return(a);
                               return(GCD(b%a,a));
              }
            static long LCM(long a,long b){
                         return ((a*b)/GCD(a,b));
               }
              static long Fermat(long a,long p){
                           long b = p-2,ans=1;
                            while(b>0){
                                 if(b%2==1)
                                      ans=(ans*a)%p;
                                       a=(a*a)%p;
                                       b=b/2;
                              }
                           return(ans);
                   }
              static void Fact(long a[],long m){
                              a[0]=1;
                           for(int i=1;i<a.length;i++)
                                   a[i]=(i*a[i-1])%m;

                      }
              static void Fact_Inv(long a[],long F[],long m){

                                 int n =a.length;
                                     a[n-1]=Fermat(F[n-1],m);
                                 for(int i=n-2;i>=0;i--)
                                        a[i]=((i+1)*a[i+1])%m;
                        }
               /*static  long d, x, y;
              static void extendedEuclid(long A, long B) {
                            if(B == 0) {
                                  d = A;
                                  x = 1;
                                  y = 0;
                              }
                           else {
                                extendedEuclid(B, A%B);
                                 long temp = x;
                                  x = y;
                                 y = temp - (A/B)*y;
                            }
                     } */
                 /*static class pair implements Comparable<pair>{
                       int x,y;
                      pair(int a,int b){
                             x=a;
                             y=b;
                       }
                     public int compareTo(pair p1)
                           { return((p1.x-p1.y)-(this.x-this.y));}
          
                   public boolean equals(Object obj) {
                         if (this == obj)
                                return true;
                        if (obj == null)
                                return false;
                        if (getClass() != obj.getClass())
                                return false;
                         pair other = (pair) obj;
                          if (x != other.x)
                                  return false;
                          if (y != other.y)
                                  return false;
                            return true;
                      }
                      @Override
                 public int hashCode() {
                      return(x-y);
                   } 
          }   */

      static void addEdge(LinkedList<Integer> adjList[],int s,int d){
                             adjList[s].add(d);
                             adjList[d].add(s);
              }
       static int abs(char x,char y)
                   { return(Math.abs(x-y));}
        static long min(long x,long y){
                     return(Math.min(x,y));
                 }
        static long max(long a,long b){
                        return Math.max(a,b);
                  }    
         static boolean correct(int n){
                          if((n&(n+1))==0)
                              return(true);
                              return(false);
                  }
           static class pair{
                        int val;
                        int l,level,bit ; // l=-1; if not any level is flipped
                        pair(int v,int L,int j,int b){
                               val = v;
                               l =L;
                               level = j;
                                bit=b;
                        }
            }
         static class FastReader 
    { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastReader() 
        { 
            br = new BufferedReader(new
                     InputStreamReader(System.in)); 
        } 
  
        String next() 
        { 
            while (st == null || !st.hasMoreElements()) 
            { 
                try
                { 
                    st = new StringTokenizer(br.readLine()); 
                } 
                catch (IOException  e) 
                { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } 
  
        int nextInt() 
        { 
            return Integer.parseInt(next()); 
        } 
  
        long nextLong() 
        { 
            return Long.parseLong(next()); 
        } 
  
        double nextDouble() 
        { 
            return Double.parseDouble(next()); 
        } 
  
        String nextLine() 
        { 
            String str = ""; 
            try
            { 
                str = br.readLine(); 
            } 
            catch (IOException e) 
            { 
                e.printStackTrace(); 
            } 
            return str; 
        } 
    } 
}