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.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class Solution {

//	public static final double EPS = 1e-9;
//	public static final int MOD = 1000000007;
//	public static final double PI = 3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679;
//	public static final int DX[] = {1, -1, 0, 0};
//	public static final int DY[] = {0, 0, 1, -1};
//	public final int sievesize = (int) (1e6);
//	public boolean[] prime;

	public static void main(String[] args) throws IOException {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		OutputWriter out = new OutputWriter(outputStream);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();
	}

	static class Task {
		
		public void solve(int testNumber, InputReader in, OutputWriter out) throws IOException {
			int k = in.nextInt();
			char[] c = in.next().toCharArray();
			int[] d = new int[c.length + 10];
			int cur = 0;
			long ans = 0;
			d[0] = 1;
			for (int i = 0; i < c.length; i++) {
				cur += c[i] - '0';
				if (cur >= k) ans += d[cur - k];
				d[cur]++;
			}
			out.println(ans, "\n");
 		}

//		static class Node {
//			String name;
//			LinkedList<Node> list;
//			
//			public Node(String name) {
//				this.name = name;
//				list = new LinkedList<>();
//			}
//		}
        
//		static class Pair<T1, T2> {   	
//	      	T1 first;
//	      	T2 second;
//		        	
//		    public Pair(T1 first, T2 second) {
//	    		this.first = first;
//				this.second = second;
//			}
//	    }
		
	}
	
//	public static void sieve(){
//		prime = new boolean[sievesize + 1];
//		Arrays.fill(prime, true);
//	    for(int x = 2; x * x < sievesize; x++)
//	    { 
//	    	if(prime[x])
//	    		for(int y = x * 2; y < sievesize; y += x) 
//	    			prime[y] = false; 
//	    }
//	}

//	public static int[] shuffle(int arr[], Random gen) {
//		for (int i = arr.length - 1; i > 0; i--) {
//            int index = gen.nextInt(i + 1);
//            int temp = arr[index];
//            arr[index] = arr[i];
//            arr[i] = temp;
//        }
//		return arr;
//	}
	
//	public static boolean triangle(long a, long b, long c){
//	    return ((a+b) > c && (b+c) >a && (a+c) > b);
//	}
	
//	public static boolean isPerfectSquare(long n){
//		if (n < 0) 
//	    	return false;
//	    long test = (long) (Math.sqrt(n) + 0.5);
//	    return test*test == n;
//	}
	
//	public static int isnum(char s){
//		if(s=='1' || s=='2' || s=='3' || s=='4' || s=='5' || s=='6' || s=='7' || s=='8' || s=='9' || s=='0') 
//	    	return 1; 
//		return 0;
//	}
	
//	public static long nextPowerOf2(long n){
//	    n--;
//	    n |= n >> 1;
//	    n |= n >> 2;
//	    n |= n >> 4;
//	    n |= n >> 8;
//	    n |= n >> 16;
//	    n++;
//	    return n;
//	}
	
//	public static int gcd(int a, int b){
//	    int t; 
//	    while (b > 0){ 
//	    	a = a % b; 
//	    	t = a; 
//	    	a = b; 
//	    	b = t; 
//    	}
//	    return a;
//	}
	
//	public static int findGcdArray(int[] arr) {
//		int min = Integer.MAX_VALUE;
//		for (int i = 0; i < arr.length; i++)
//			min = Math.min(min, arr[i]);
//		while (min > 1) {
//			int i = 0, s = 0;
//			while (i < arr.length) {
//				s += arr[i] % min;
//				i++;
//			}
//			if (s == 0) return min;
//			min--;
//		}
//		return 1;
//	}

	static class InputReader {
		public BufferedReader reader;
		public StringTokenizer tokenizer;

		public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		}
		
		private void tokenize() {
			while (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
		}

		public String next() {
			tokenize();
			return tokenizer.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

		public long nextLong() {
			return Long.parseLong(next());
		}
		
		public char nextChar() {
			return next().charAt(0);
		}
		
		public float nextFloat() {
			return Float.parseFloat(next());
		}
		
		public double nextDouble() {
			return Double.parseDouble(next());
		}

		public int[] nextIntArray(int size) {
			tokenize();
			int[] arr=new int[size];
			for(int i = 0; i < size; i++) {
				tokenize();
				arr[i] = Integer.parseInt(tokenizer.nextToken());
			}
			return arr;
		}
		
		public long[] nextLongArray(int size) {
			tokenize();
			long[] arr=new long[size];
			for(int i = 0; i < size; i++) {
				tokenize();
				arr[i] = Long.parseLong(tokenizer.nextToken());
			}
			return arr;
		}
		
		public float[] nextFloatArray(int size) {
			tokenize();
			float[] arr=new float[size];
			for(int i = 0; i < size; i++) {
				tokenize();
				arr[i] = Float.parseFloat(tokenizer.nextToken());
			}
			return arr;
		}

		public double[] nextDoubleArray(int size) {
			tokenize();
			double[] arr=new double[size];
			for(int i = 0; i < size; i++) {
				tokenize();
				arr[i] = Double.parseDouble(tokenizer.nextToken());
			}
			return arr;
		}

		public String[] nextStringArray(int size) throws IOException {
			String[] arr=new String[size];
			for(int i = 0; i < size; i++) 
				arr[i] = reader.readLine();
			return arr;
		}

		public char[] nextCharArray(int size) throws IOException {
			return reader.readLine().toCharArray();
		}
	}

	static class OutputWriter {
		public PrintWriter pw;

		public OutputWriter(OutputStream stream) {
			pw = new PrintWriter(stream);
		}
		
		public void println(Object... obj) {
			if (obj.length == 0) pw.println();
			else {
				String delimiter = (String) obj[obj.length - 1];
				for (int i = 0 ; i < obj.length - 2; i++) {
					pw.print(obj[i]);
					pw.print(delimiter);
				}
				pw.println(obj[obj.length - 2]);
			}
		}

		public void close() {
			pw.close();
		}

		public void flush() {
			pw.flush();
		}

		public void printStringArray(String[] arr) {
			for(int i = 0; i < arr.length; i++)
				pw.println(arr[i]);
		}

		public void printIntArray(int[] arr) {
			for(int i = 0; i < arr.length; i++)
				pw.print(arr[i] + " ");
		}

		public void printLongArray(long[] arr) {
			for(int i = 0; i < arr.length; i++)
				pw.print(arr[i] + " ");
		}

		public void printCharArray(char[] arr) {
			for(int i = 0; i < arr.length; i++)
				pw.print(arr[i] + " ");
		}

		public void printFloatArray(float[] arr) {
			for(int i = 0; i < arr.length; i++)
				pw.print(arr[i] + " ");
		}

		public void printDoubleArray(double[] arr) {
			for(int i = 0; i < arr.length; i++)
				pw.print(arr[i] + " ");
		}
	}
}