using System.Collections;
using System.Text;
using System.Threading.Tasks;
using static System.Math;
using static System.Console;
using System.Collections.Generic;
using System.Linq;
using System;
using System.Numerics;

class Program
{
    #region Reader
    //static Vector2Int ReadVec2Int
    //{
    //    get
    //    {
    //        string[] s = Console.ReadLine().Split(' ');
    //        return new Vector2Int(int.Parse(s[0]), int.Parse(s[1]));
    //    }
    //}
    //static Vector2Int[] ReadVec2Ints(int n)
    //{
    //    List<Vector2Int> list = new List<Vector2Int>();
    //    for (int i = 0; i < n; ++i)
    //    {
    //        var ab = ReadInts;
    //        list.Add(new Vector2Int(ab[0], ab[1]));
    //    }
    //    return list.ToArray();
    //}
    //static HashSet<Vector2Int> ReadVec2IntHash(int n)
    //{
    //    HashSet<Vector2Int> hash = new HashSet<Vector2Int>();
    //    for (int i = 0; i < n; ++i)
    //    {
    //        var ab = ReadInts;
    //        hash.Add(new Vector2Int(ab[0], ab[1]));
    //    }
    //    return hash;
    //}
    static string ReadStr => Console.ReadLine();
    static string[] ReadStrs => Console.ReadLine().Split(' ');
    static int ReadInt => Convert.ToInt32(Console.ReadLine());
    static int[] ReadInts => Console.ReadLine().Split(' ').Select(s => Convert.ToInt32(s)).ToArray();
    static long ReadLong => Convert.ToInt64(Console.ReadLine());
    static long[] ReadLongs => Console.ReadLine().Split(' ').Select(s => Convert.ToInt64(s)).ToArray();
    static long[,] ReLongMatrix(int r, int c)
    {
        var mat = new long[r, c];
        for (int i = 0; i < r; ++i)
        {
            var x = ReadLongs;
            for (int j = 0; j < c; ++j)
            {
                mat[i, j] = x[j];
            }
        }
        return mat;
    }
    static Tuple<string, string>[] ReTupleStr(int n)
    {
        List<Tuple<string, string>> list = new List<Tuple<string, string>>();
        for (int i = 0; i < n; ++i)
        {
            var ab = ReadStrs;
            list.Add(new Tuple<string, string>(ab[0], ab[1]));
        }
        return list.ToArray();
    }
    static Tuple<long, long>[] ReTupleLong(int n)
    {
        List<Tuple<long, long>> list = new List<Tuple<long, long>>();
        for (int i = 0; i < n; ++i)
        {
            var ab = ReadLongs;
            list.Add(new Tuple<long, long>(ab[0], ab[1]));
        }
        return list.ToArray();
    }
    static Tuple<int, int>[] ReadTupleInt(int n)
    {
        List<Tuple<int, int>> list = new List<Tuple<int, int>>();
        for (int i = 0; i < n; ++i)
        {
            var ab = ReadInts;
            list.Add(new Tuple<int, int>(ab[0], ab[1]));
        }
        return list.ToArray();
    }
    static Tuple<double, double>[] ReTupleDouble(int n)
    {
        List<Tuple<double, double>> list = new List<Tuple<double, double>>();
        for (int i = 0; i < n; ++i)
        {
            var ab = ReadLongs;
            list.Add(new Tuple<double, double>(ab[0], ab[1]));
        }
        return list.ToArray();
    }
    static Dictionary<int, HashSet<int>> ReAdjacencyList(int N, int M)
    {
        Dictionary<int, HashSet<int>> dict = new Dictionary<int, HashSet<int>>();
        for (int i = 0; i <= N; ++i)
        {
            dict.Add(i, new HashSet<int>());
        }
        for (int i = 0; i < M; ++i)
        {
            var ab = ReadInts;
            dict[ab[0]].Add(ab[1]);
            dict[ab[1]].Add(ab[0]);
        }
        return dict;
    }
    #endregion
    static void Swap<T>(ref T a, ref T b)
    {
        T temp = a;
        a = b;
        b = temp;
    }
    static long mod = (int)Pow(10, 9) + 7;

    static void Main()
    {
        int[] NK = ReadInts;
        int N = NK[0];
        int K = NK[1];

        string S = ReadStr;

        List<Tuple<char, int>> p = new List<Tuple<char, int>>();

        int index = 0;
        char stand = S[0];
        int num = 0;


        int max = 0;
        while (index<N)
        {
            if (S[index]== stand) num++;
            else
            {
                p.Add(new Tuple<char, int>(stand, num));
                num = 1;
                if (stand == '0') max++;
                stand = S[index];
            }
            index++;
        }
        p.Add(new Tuple<char, int>(stand, num));
        if (stand == '0') max++;


        if (K >= max)
        {
            WriteLine(N);
            return;
        }

        int first = S[0]-'0'==1?0:1;

        int l = first;
        int r = first + 2*K + 1;

        List<int> cnts = new List<int>() { 0};

        for (int i = l; i < r; i++)
        {
            if (i >= p.Count) break;
            cnts[0] += p[i].Item2;
        }

        r += 2;
        l += 2;

        while (r<=p.Count)
        {
            int test = cnts[cnts.Count-1];

            test -= p[l - 2].Item2;
            test -= p[l - 1].Item2;
            test += p[r - 2].Item2;
            test += p[r - 1].Item2;

            cnts.Add(test);

            l += 2;
            r += 2;
        }


        if (S[0] == '0')
        {
            cnts.Add(0);
            for (int i = 0; i < 2*K; i++)
            {
                cnts[cnts.Count - 1] += p[i].Item2;
            }
        }

        if (S[S.Length-1] == '0')
        {
            cnts.Add(0);
            for (int i = 0; i < 2 * K; i++)
            {
                cnts[cnts.Count - 1] += p[p.Count-i-1].Item2;
            }
        }

        WriteLine(cnts.Max());
    }
}


Measured memory_bytes: 15968