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.util.*;
import java.math.*;
import java.lang.*;

public class Main implements Runnable 
{
    static class InputReader 
    {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private SpaceCharFilter filter;
        private BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        public InputReader(InputStream stream) 
        {
            this.stream = stream;
        }
        
        public int read()
        {
            if (numChars==-1) 
                throw new InputMismatchException();
            
            if (curChar >= numChars) 
            {
                curChar = 0;
                try
                {
                    numChars = stream.read(buf);
                }
                catch (IOException e)
                {
                    throw new InputMismatchException();
                }
                
                if(numChars <= 0)               
                    return -1;
            }
            return buf[curChar++];
        }
    
        public String nextLine()
        {
            String str = "";
            try
            {
                str = br.readLine();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }    
            return str;
        }
        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 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 double nextDouble() 
        {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-')
            {
                sgn = -1;
                c = read();
            }
            double res = 0;
            while (!isSpaceChar(c) && c != '.') 
            {
                if (c == 'e' || c == 'E')
                    return res * Math.pow(10, nextInt());
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            if (c == '.') 
            {
                c = read();
                double m = 1;
                while (!isSpaceChar(c))
                {
                    if (c == 'e' || c == 'E')
                        return res * Math.pow(10, nextInt());
                    if (c < '0' || c > '9')
                        throw new InputMismatchException();
                    m /= 10;
                    res += (c - '0') * m;
                    c = read();
                }
            }
            return res * sgn;
        }
    
        public String readString() 
        {
            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 boolean isSpaceChar(int c) 
        {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
    
        public String next()
        {
            return readString();
        }
        
        public interface SpaceCharFilter
        {
            public boolean isSpaceChar(int ch);
        }
    }
    public static void main(String args[]) throws Exception 
    {
        new Thread(null, new Main(),"Main",1<<27).start();
    }
    
    static class Pair{
        int f;
        int s;
        PrintWriter w;

        //int t;
        
        
        // Pair(int f,int s,int t){
        Pair(int f,int s, PrintWriter w){
            this.f = f;
            this.s = s;
            this.w = w;
            //this.t = t;
            
        }
        
        public static Comparator<Pair> wc = new Comparator<Pair>(){
            public int compare(Pair e1,Pair e2){
            
                //1 for swap 
                if(Math.abs(e1.f)-Math.abs(e2.f)!=0){
                    //e1.w.println("**"+e1.f+" "+e2.f);
                    return (Math.abs(e1.f)-Math.abs(e2.f));
                }
                else{
                    //e1.w.println("##"+e1.f+" "+e2.f);
                    return (Math.abs(e1.s)-Math.abs(e2.s));
                }

                
            }
        };	
    }

    public static long gcd(long a,long b){
        if(b==0)return a;
        else return gcd(b,a%b);
    }


    ////recursive BFS
    public static int bfsr(int s,ArrayList<Integer>[] a,boolean[] b,int[] pre){
        b[s]=true;
        int p = 1;
        int n = pre.length -1;
        int t = a[s].size();
        int max = 1;
        for(int i=0;i<t;i++){
            int x = a[s].get(i);
            if(!b[x]){
                //dist[x] = dist[s] + 1;
                int xz =  (bfsr(x,a,b,pre));
                p+=xz;
                max = Math.max(xz,max);
            }
        }
        //max = Math.max(max,(n-p));
        pre[s] = max;
        return p;
    }   

//// iterative BFS
    public static int bfs(int s,ArrayList<Integer>[] a,int dist,boolean[] b,PrintWriter w){
        b[s]=true;
        int siz = 0;
        dist--;
        Queue<Integer> q = new LinkedList<>();
        q.add(s);
        while(q.size()!=0 && dist>0 ){
            int i=q.poll();
            Iterator<Integer> it = a[i].listIterator();
            int z=0;
            while(it.hasNext() && dist>0){
                z=it.next();
                if(!b[z]){
                    b[z]=true;
                    dist--;
                    //dist[z] = dist[i] + 1;
                    siz++;
                    q.add(z);
                }
            }   
        
        }
        return siz;
    }

    public static int lower(int key, Integer[] a){
        int l = 0;
        int r = a.length-1;
        int res = 0;

        while(l<=r){
            int mid = (l+r)/2;

            if(a[mid]<=key){
                l = mid+1;
                res = mid+1;
            }
            else{
                r = mid -1;
            }
        }

        return res;
    }

    

    

//////////////////////////////////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////////////////////////////////


    public void run()
    {
        InputReader sc = new InputReader(System.in);
        PrintWriter w = new PrintWriter(System.out);
        int defaultValue = 0;
        long mod = Long.valueOf("1000000007");

        
        // int tc = sc.nextInt();
        // while(tc-->0){

            //int n = sc.nextInt();
            int k = sc.nextInt();
            char[] a = sc.next().toCharArray();
            int n = a.length;
            long c = 0;
            int o = 0;
            long z = 0;
            long[] x = new long[n+2];
            for(int i=0;i<n;i++){
                if(a[i]=='1'){
                    z += (c*(c+1))/2;
                    x[o] = c+1;
                    c = 0;
                    o++;
                }
                else c++;
            }
            z += (c*(c+1))/2;
            x[o] = c+1;
            o++;
            // w.print("* ");
            // for(int i=0;i<o;i++){
            //     w.print(x[i]+" ");
            // }
            // w.println("");
            long ans = 0;
            for(int i=k;i<o;i++){
                int j = i-k;
                ans+= ( x[i]*x[j]);
            }
            if(k>0)
                w.println(ans);
            else 
                w.println(z);




            


            
            

            
       // }
        w.flush();
        w.close();
    }
    
    
    

    
}

