using System;
using System.IO;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Numerics;


partial class Solver
{
    public struct Data
    {
        public char C;
        public int N;
    }

    public static Data[] Compress(string s)
    {
        int cur = 0;
        var result = new List<Data>();
        while (cur < s.Length)
        {
            int i = cur;
            while (cur < s.Length && s[i] == s[cur]) cur++;
            result.Add(new Data { N = cur - i, C = s[i] });
        }
        return result.ToArray();
    }

    public void Run()
    {
        var N = ni();
        var K = ni();
        var S = ns();
        var d = Compress(S);
        var sum = d.Select(x => x.N).ToArray();
        for (int i = 1; i < sum.Length; i++)
        {
            sum[i] += sum[i - 1];
        }

        int ans = 0;

        if (!S.Contains('0')) ans = S.Length;

        for (int i = 0; i < d.Length; i++)
        {
            if (d[i].C == '0')
            {
                var k = 0;

                k = sum[Math.Min(i + 2 * (K - 1) + 1, sum.Length - 1)];
                if (i - 2 >= 0) k -= sum[i - 2];

                ans = Math.Max(ans, k);
            }
        }

        cout.WriteLine(ans);
    }
}




// PREWRITEN CODE BEGINS FROM HERE
partial class Solver : Scanner
{
    public static void Main(string[] args)
    {
        new Solver(Console.In, Console.Out).Run();
    }

    TextReader cin;
    TextWriter cout;

    public Solver(TextReader reader, TextWriter writer)
        : base(reader)
    {
        this.cin = reader;
        this.cout = writer;
    }
    public Solver(string input, TextWriter writer)
        : this(new StringReader(input), writer)
    {
    }

    public int ni() { return NextInt(); }
    public int[] ni(int n) { return NextIntArray(n); }
    public long nl() { return NextLong(); }
    public long[] nl(int n) { return NextLongArray(n); }
    public double nd() { return NextDouble(); }
    public string ns() { return Next(); }
}

public class Scanner
{
    private TextReader Reader;
    private Queue<String> TokenQueue = new Queue<string>();
    private CultureInfo ci = CultureInfo.InvariantCulture;

    public Scanner()
        : this(Console.In)
    {
    }

    public Scanner(TextReader reader)
    {
        this.Reader = reader;
    }

    public int NextInt() { return Int32.Parse(Next(), ci); }
    public long NextLong() { return Int64.Parse(Next(), ci); }
    public double NextDouble() { return double.Parse(Next(), ci); }
    public string[] NextArray(int size)
    {
        var array = new string[size];
        for (int i = 0; i < size; i++) array[i] = Next();
        return array;
    }
    public int[] NextIntArray(int size)
    {
        var array = new int[size];
        for (int i = 0; i < size; i++) array[i] = NextInt();
        return array;
    }

    public long[] NextLongArray(int size)
    {
        var array = new long[size];
        for (int i = 0; i < size; i++) array[i] = NextLong();
        return array;
    }

    public String Next()
    {
        if (TokenQueue.Count == 0)
        {
            if (!StockTokens()) throw new InvalidOperationException();
        }
        return TokenQueue.Dequeue();
    }

    public bool HasNext()
    {
        if (TokenQueue.Count > 0)
            return true;
        return StockTokens();
    }

    private bool StockTokens()
    {
        while (true)
        {
            var line = Reader.ReadLine();
            if (line == null) return false;
            var tokens = line.Trim().Split(" ".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);
            if (tokens.Length == 0) continue;
            foreach (var token in tokens)
                TokenQueue.Enqueue(token);
            return true;
        }
    }
}


Measured memory_bytes: 16224