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.util.*;
import java.io.*;
public class Practice {

	//static int a[], b[],c[];
	//static long d[];
	//static int m,ans;
	static ArrayList<Pair> adj[];
	//static int cat[];
	static boolean visited[];
	static boolean b[];
	public static void main(String[] args) {
		
		
		in=new InputReader(System.in);
		w=new PrintWriter(System.out);
		int k=in.nextInt();
		String s=in.nextLine();
		int fresum[]=new int[s.length()+1];
		int sum=0;
		fresum[0]=1;
		long seg=0;
		for(int i=0;i<s.length();i++)
		{
			sum+=(s.charAt(i)-'0');
			if(sum-k>=0) 
				seg+=fresum[sum-k];
			fresum[sum]++;
		}
		w.println(seg);
		w.close();
				
	}
	static  int dfs(int u,int v,int color)
	{
		if(u==v)
			return 1;
		visited[u]=true;
		for(Pair p : adj[u])
		{
			if(p.c==color && !visited[p.edge])
			{		if(dfs(p.edge,v,color)==1)
					return 1;
		}
		}
		return 0;
			
	}
	static InputReader in;
	static PrintWriter w;
	public static void seive(long n){
		b = new boolean[(int) (n+1)];
		Arrays.fill(b, true);
		for(int i = 2;i*i<=n;i++){
			if(b[i]){
				for(int p = 2*i;p<=n;p+=i){
					b[p] = false;
				}
			}
		}
	}
	static class Pair implements Comparable<Pair> {
		int edge;
		int c;
		public Pair(){
			
		}
		public Pair(int u, int v) {
			this.edge = u;
			this.c= v;
			
		}
		
	//	public int hashCode() {
		//	int hu = (int) (u ^ (u >>> 32));
			//int hv = (int) (v ^ (v >>> 32));
			//return 31*hu + hv;
	//	}

	/*	public boolean equals(Object o) {
			Pair other = (Pair) o;
			return (u == other.u && v == other.v);
		}*/

		public int compareTo(Pair other) {
			
				return 0;
		}
		
		/*public String toString() {
			return "[u=" + u + ", v=" + v + "]";
		}*/
	}
	static class Node2{
		Node2 left = null;
		Node2 right = null;
		Node2 parent = null;
		int data;
	}
	
	//binaryStree
	static class BinarySearchTree{
		Node2 root = null;
		int height = 0;
		int max = 0;
		int cnt = 1;
		ArrayList<Integer> parent = new ArrayList<>();
		HashMap<Integer, Integer> hm = new HashMap<>();
		public void insert(int x){
			Node2 n = new Node2();
			n.data = x;
			if(root==null){
				root = n;
			}
			else{
				Node2 temp = root,temp2 = null;
				while(temp!=null){
					temp2 = temp;
					if(x>temp.data) temp = temp.right;
					else temp = temp.left;
				}
				if(x>temp2.data) temp2.right = n;
				else temp2.left = n;
				n.parent = temp2;
				parent.add(temp2.data);
			}
		}
		public Node2 getSomething(int x, int y, Node2 n){
			if(n.data==x || n.data==y) return n;
			else if(n.data>x && n.data<y) return n;
			else if(n.data<x && n.data<y) return getSomething(x,y,n.right);
			else return getSomething(x,y,n.left);
		}
		public Node2 search(int x,Node2 n){
			if(x==n.data){
				max = Math.max(max, n.data);
				return n;
			}
			if(x>n.data){
				max = Math.max(max, n.data);
				return search(x,n.right);
			}
			else{
				max = Math.max(max, n.data);
				return search(x,n.left);
			}
		}
		public int getHeight(Node2 n){
			if(n==null) return 0;
			height = 1+ Math.max(getHeight(n.left), getHeight(n.right));
			return height;
		}
	}
public static void debug(Object... o) {
	System.out.println(Arrays.deepToString(o));
}

public static String rev(String s)
{
	StringBuilder sb=new StringBuilder(s);
	sb.reverse();
	return sb.toString();
}

static long lcm(long a, long b)
{
    return a * (b / gcd(a, b));
}

static long gcd(long a, long b)
{
    while (b > 0)
    {
        long temp = b;
        b = a % b; // % is remainder
        a = temp;
    }
    return a;
}

public static long max(long x, long y, long z){
		if(x>=y && x>=z) return x;
		if(y>=x && y>=z) return y;
		return z;
	}
	static int[] sieve(int n,int[] arr)
	{
	for(int i=2;i*i<=n;i++)
	{
		if(arr[i]==0)
		{
			for(int j=i*2;j<=n;j+=i)
				arr[j]=1;
		}
	}
	return arr;
	}




static class InputReader {

private final InputStream stream;
private final 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) {
	 return nextIntArray(n, 0);
	    }
	    
public int[] nextIntArray(int n, int off) {
	 int[] arr = new int[n + off];
	   for (int i = 0; i < n; i++) {
	    arr[i + off] = nextInt();
	    }
	    return arr;
	    }
	    
public long[] nextLongArray(int n) {
return nextLongArray(n, 0);
	    }
        
	public long[] nextLongArray(int n, int off) {
	 long[] arr = new long[n + off];
	 for (int i = 0; i < n; i++) {
		  arr[i + off] = nextLong();
		 }
 return arr;
	}


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 String nextLine() {
  int c = snext();
  while (isSpaceChar(c))
    c = snext();
  StringBuilder res = new StringBuilder();
  do {
    res.appendCodePoint(c);
    c = snext();
  } while (!isEndOfLine(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;
}

private boolean isEndOfLine(int c) {
  return c == '\n' || c == '\r' || c == -1;
}

public interface SpaceCharFilter {
  public boolean isSpaceChar(int ch);
}
}
	
}
