import java.util.*;
import java.io.*;
public class Main {
    public static void main(String[] args) {
        FastScanner sc = new FastScanner();
        int n = sc.nextInt();
        int k = sc.nextInt();
        String s = sc.next();
        List<Integer> num = new ArrayList<>();
        int now = 1;
        int cnt = 0;
        for (int i = 0; i < n; i++) {
            char ch = s.charAt(i);
            if (ch == '0' + now) {
                cnt++;
            } else {
                num.add(cnt);
                now = 1 - now;
                cnt = 1;
            }
        }
        if (cnt != 0) {
            num.add(cnt);
        }
        if (num.size() % 2 == 0) {
            num.add(0);
        }

        int add = 2 * k + 1;
        int[] sum = new int[num.size() + 1];
        for (int i = 0; i < num.size(); i++) {
            sum[i + 1] = sum[i] + num.get(i);
        }
        int ans = 0;
        for (int i = 0; i < num.size(); i += 2) {
            int left = i;
            int right = Math.min(i + add, num.size());
            int tmp = sum[right] - sum[left];
            ans = Math.max(tmp, ans);
        }
        System.out.println(ans);
    }
}

class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() {
        if (hasNextByte())
            return buffer[ptr++];
        else
            return -1;
    }
    private static boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    }
    public boolean hasNext() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;
        return hasNextByte();
    }
    public String next() {
        if (!hasNext())
            throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }
    public long nextLong() {
        if (!hasNext())
            throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
            throw new NumberFormatException();
        return (int) nl;
    }
    public double nextDouble() {
        return Double.parseDouble(next());
    }
}


Measured memory_bytes: 25300