using System;
using System.Collections.Generic;

public class Program
{
    private int N, K;
    private string S;
    private List<int> L;

    public void Solve()
    {
        var sc = new Scanner();
        N = sc.NextInt();
        K = sc.NextInt();
        S = sc.Next();

        L = new List<int>();

        char c = '1';
        L.Add(0);

        foreach (char c1 in S)
        {
            if (c1 != c)
            {
                c = c1;
                L.Add(0);
            }

            L[L.Count - 1]++;
        }

        if (c == '0')
        {
            L.Add(0);
        }

        // 1 0 1 0 1 0 1

        if (L.Count <= K * 2 + 1)
        {
            Console.WriteLine(N);
            return;
        }

        int tmp = L[0];

        int index = 1;

        for (int i = 0; i < K; i++)
        {
            tmp += L[index];
            tmp += L[index + 1];
            index += 2;
        }

        int ans = tmp;

        // index = 1 + 2 * K

        for (; index + 1 < L.Count; index += 2)
        {
            tmp += L[index];
            tmp += L[index + 1];
            tmp -= L[index - 2 * K - 1];
            tmp -= L[index - 2 * K];
            ans = Math.Max(ans, tmp);
        }
        
        Console.WriteLine(ans);
    }

    public static void Main(string[] args)
    {
        new Program().Solve();
    }
}

class Scanner
{
    public Scanner()
    {
        _pos = 0;
        _line = new string[0];
    }

    const char Separator = ' ';
    private int _pos;
    private string[] _line;

    #region スペース区切りで取得

    public string Next()
    {
        if (_pos >= _line.Length)
        {
            _line = Console.ReadLine().Split(Separator);
            _pos = 0;
        }

        return _line[_pos++];
    }

    public int NextInt()
    {
        return int.Parse(Next());
    }

    public long NextLong()
    {
        return long.Parse(Next());
    }

    public double NextDouble()
    {
        return double.Parse(Next());
    }

    #endregion

    #region 型変換

    private int[] ToIntArray(string[] array)
    {
        var result = new int[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = int.Parse(array[i]);
        }

        return result;
    }

    private long[] ToLongArray(string[] array)
    {
        var result = new long[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = long.Parse(array[i]);
        }

        return result;
    }

    private double[] ToDoubleArray(string[] array)
    {
        var result = new double[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = double.Parse(array[i]);
        }

        return result;
    }

    #endregion

    #region 配列取得

    public string[] Array()
    {
        if (_pos >= _line.Length)
            _line = Console.ReadLine().Split(Separator);

        _pos = _line.Length;
        return _line;
    }

    public int[] IntArray()
    {
        return ToIntArray(Array());
    }

    public long[] LongArray()
    {
        return ToLongArray(Array());
    }

    public double[] DoubleArray()
    {
        return ToDoubleArray(Array());
    }

    #endregion
}

Measured memory_bytes: 13236