Problem:
Score : 400 points

Problem Statement

N people are arranged in a row from left to right.

You are given a string S of length N consisting of 0 and 1, and a positive integer K.

The i-th person from the left is standing on feet if the i-th character of S is 0, and standing on hands if that character is 1.

You will give the following direction at most K times (possibly zero):

Direction: Choose integers l and r satisfying 1 \leq l \leq r \leq N, and flip the l-th, (l+1)-th, ..., and r-th persons. That is, for each i = l, l+1, ..., r, the i-th person from the left now stands on hands if he/she was standing on feet, and stands on feet if he/she was standing on hands.

Find the maximum possible number of consecutive people standing on hands after at most K directions.

Constraints

N is an integer satisfying 1 \leq N \leq 10^5.

K is an integer satisfying 1 \leq K \leq 10^5.

The length of the string S is N.

Each character of the string S is 0 or 1.

Input

Input is given from Standard Input in the following format:

N K
S

Output

Print the maximum possible number of consecutive people standing on hands after at most K directions.

Sample Input 1

5 1
00010

Sample Output 1

4

We can have four consecutive people standing on hands, which is the maximum result, by giving the following direction:

Give the direction with l = 1, r = 3, which flips the first, second and third persons from the left.

Sample Input 2

14 2
11101010110011

Sample Output 2

8

Sample Input 3

1 1
1

Sample Output 3

1

No directions are necessary.

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;

class ABC124D{
    public static void Main(){
        var NK = Console.ReadLine().Split().Select(int.Parse);
        var Sin = Console.ReadLine().ToCharArray();
        var Si = new List<int>();
        var Sb = new List<bool>();
        var count = 0;
        var bef = Sin[0] == '1';
        var t = true;
        for(var index = 0;index<Sin.Length;index++){
            t = Sin[index]=='1';
            if(bef == t){
                count++;
            }else{
                Si.Add(count);
                Sb.Add(bef);
                bef=t;
                count = 1;
            }
        }
        Si.Add(count);
        Sb.Add(t);
        var max = 0;
        var sum = 0;
        if(NK.ElementAt(1)*2>Si.Count){
            Console.WriteLine(Si.Sum());
            return;
        }
        for(var index = 0;index+NK.ElementAt(1)*2<Si.Count;index++){
            var take = NK.ElementAt(1)*2+(Sb[index]?1:0);
            sum = Si.Skip(index).Take(take).Sum();
            if(max<sum)max = sum;
        }
        Console.WriteLine(max);
    }
}