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.lang.*;
import java.io.*;
import java.math.*;

public class Codeforces {

    static double Phi = (1 + Math.sqrt(5)) / 2.0;
    static int MAX = -1 >>> 1;
    static long MODL = 1_000_000_007L;
    static int MOD = 1_000_000_007;
    static void no() throws IOException {println("NO");}
    static void yes() throws IOException {println("YES");}

    static boolean testCases = false;
    static boolean DEBUG = true;

    static void main() throws Exception {
        int k = ni();
        char[] s = line().toCharArray();
        int n = s.length;
        List<Long> zeros = new ArrayList<>();
    
        int[] left = new int[n];
        int[] right = new int[n];
        int lc = 0, rc = 0;
        int onec = 0;
        for (int i = 0; i < n; ++i) {
            if(s[i] == '1') {
                ++onec;
                zeros.add((long) lc);
                left[i] = lc;
                lc = 0;
            } else {
                ++lc;
            }
        }
        if(lc != 0) zeros.add((long) lc);
        if(k == 0) {
            long ans = 0;
            for(long ele : zeros) {
                ans += (ele * (ele + 1L)) >> 1;
            }
            println(ans);
            return;
        }
        for (int i =  n - 1; i >= 0; --i) {
            if(s[i] == '1') {
                right[i] = rc;
                rc = 0;
            } else {
                ++rc;
            }
        }
        //need atleast k ones to solve problem
        if(onec < k) {
            println(0);
            return;
        }
        //set l and r
        int l = getOne(s, 0);
        int r = l;
        int kc = k - 1;
        long ans = 0; 
        while(kc-- > 0) {
            ++r;
            r = getOne(s, r);
            assert r != -1;
        }
        while(l != -1 && r != -1) {
            //have valid l and r
            //find their answer
            long p1 = left[l] + 1;
            long p2 = right[r] + 1;
            ans += p1 * p2;
            debug("adding " + (p1 * p2) + " for l = " + l + ", r = " + r);
            l = getOne(s, l + 1);
            r = getOne(s, r + 1);
        }
        println(ans);
    }
    static int getOne(char[] s, int from) {
        for(int i = from; i < s.length; ++i) {
            if(s[i] == '1') return i;
        }
        return -1;
    }
    
    public static void main(String[] args) throws Exception {
        long startPointTime = System.currentTimeMillis();
        scannerIn = System.in;
        printerBW = new BufferedWriter(new OutputStreamWriter(System.out));
        if (DEBUG && System.getProperty("ONLINE_JUDGE") == null) {
            HABLA = true;
            debug("Debugging enabled");
        }

        int t = testCases ? ni() : 1;
        int to = t;
        while (t-- > 0) {
            debug("Case #" + (to - t) + " ---------------- ");
            main();
        }
        long endTime = System.currentTimeMillis();
        float totalProgramTime = endTime - startPointTime;
        if (HABLA)
            debug("Execution time is " + totalProgramTime + " (" + (totalProgramTime / 1000) + "s)");
        close();
    }
    
 //IO Stuff
    private static boolean HABLA = false;
    private static byte[] scannerByteBuffer = new byte[1024]; // Buffer of Bytes
    private static int scannerIndex;
    private static InputStream scannerIn;
    private static int scannerTotal;
    private static BufferedWriter printerBW;

    private static int next() throws IOException { // Scan method used to scan buf
        if (scannerTotal < 0)
            throw new InputMismatchException();
        if (scannerIndex >= scannerTotal) {
            scannerIndex = 0;
            scannerTotal = scannerIn.read(scannerByteBuffer);
            if (scannerTotal <= 0)
                return -1;
        }
        return scannerByteBuffer[scannerIndex++];
    }

    static int ni() throws IOException {
        int integer = 0;
        int n = next();
        while (isWhiteSpace(n)) // Removing startPointing whitespaces
            n = next();
        int neg = 1;
        if (n == '-') { // If Negative Sign encounters
            neg = -1;
            n = next();
        }
        while (!isWhiteSpace(n)) {
            if (n >= '0' && n <= '9') {
                integer *= 10;
                integer += n - '0';
                n = next();
            } else
                throw new InputMismatchException();
        }
        return neg * integer;
    }

    static long nl() throws IOException {
        long integer = 0;
        int n = next();
        while (isWhiteSpace(n)) // Removing startPointing whitespaces
            n = next();
        int neg = 1;
        if (n == '-') { // If Negative Sign encounters
            neg = -1;
            n = next();
        }
        while (!isWhiteSpace(n)) {
            if (n >= '0' && n <= '9') {
                integer *= 10;
                integer += n - '0';
                n = next();
            } else
                throw new InputMismatchException();
        }
        return neg * integer;
    }

    static String line() throws IOException {
        StringBuilder sb = new StringBuilder();
        int n = next();
        while (isWhiteSpace(n))
            n = next();
        while (!isNewLine(n)) {
            sb.append((char) n);
            n = next();
        }
        return sb.toString();
    }

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

    private static boolean isWhiteSpace(int n) {
        return n == ' ' || isNewLine(n) || n == '\t';
    }

    static int[] nia(int n) throws Exception {
        if (n < 0)
            throw new Exception("Array size should be non negative");
        int[] array = new int[n];
        for (int i = 0; i < n; i++)
            array[i] = ni();
        return array;
    }

    static long[] nla(int n) throws Exception {
        if (n < 0)
            throw new Exception("Array size should be non negative");
        long[] array = new long[n];
        for (int i = 0; i < n; i++)
            array[i] = nl();
        return array;
    }

    static float[] nfa(int n) throws Exception {
        if (n < 0)
            throw new Exception("Array size should be non negative");
        float[] array = new float[n];
        for (int i = 0; i < n; i++)
            array[i] = nl();
        return array;
    }

    static double[] nda(int n) throws Exception {
        if (n < 0)
            throw new Exception("Array size should be non negative");
        double[] array = new double[n];
        for (int i = 0; i < n; i++)
            array[i] = nl();
        return array;
    }

    static <T> void print(T str) throws IOException {
        printerBW.append(str.toString());
        if (HABLA) flush();
    }

    static <T> void println() throws IOException {
        printerBW.append('\n');
        if (HABLA) flush();
    }

    static <T> void println(T str) throws IOException {
        if (str == null) {
            printerBW.append("null\n");
        } else {
            printerBW.append(str.toString());
            printerBW.append('\n');
            if (HABLA) flush();
        }
    }

    public static final String ANSI_RESET = "\u001B[0m";
    public static final String ANSI_DEBUG = "\u001B[33m";
    static <T> void debugl(T str) throws IOException {
        if (!HABLA) return;
        if (str == null) {
            printerBW.append(ANSI_DEBUG);
            printerBW.append("null");
            printerBW.append(ANSI_RESET);
        } else {
            printerBW.append(ANSI_DEBUG);
            printerBW.append(str.toString());
            printerBW.append(ANSI_RESET);
        }
        flush();
    }

    static void debug() throws IOException {
        if (!HABLA) return;
        printerBW.append('\n');
        flush();
    }
    static <T> void debug(T str) throws IOException {
        if (!HABLA) return;
        if (str == null) {
            printerBW.append(ANSI_DEBUG);
            printerBW.append("null\n");
            printerBW.append(ANSI_RESET);
        } else {
            printerBW.append(ANSI_DEBUG);
            printerBW.append(str.toString());
            printerBW.append(ANSI_RESET);
            printerBW.append('\n');
        }
        flush();
    }

    static void flush() throws IOException {
        printerBW.flush();
    }

    static void close() {
        try {
            printerBW.close();
        } catch (IOException e) {
            System.out.println(e.toString());
        }
    }
}
