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;
class Program
{
	static void Main(string[] args)
	{
		string[] str = Console.ReadLine().Split();
		int N = int.Parse(str[0]);
		int K = int.Parse(str[1]);
		string s = Console.ReadLine();
		var list = new List<int>();
		var t1 = 0;
		var f = 1;
		var t2 = 0;
		int ct = 0;
		list.Add(0);
		int ans = 0;
		for(var i=0;i<N;i++){
			string s1 = s.Substring(i,1);
			if(f==1 && s1 == "0"){
				f=0;
				if(ct-K>=0){
					ans = Math.Max(ans,i-list[ct-K]);
				}
			} else if(f==0 && s1 == "1"){
				f=1;
				list.Add(i);
				ct++;
			}
		}
		if(f==1 && ct-K>=0){
			ans = Math.Max(ans,N-1-list[ct-K]+1);
		} else if(ct-K+1>=0){
			ans = Math.Max(ans,N-1-list[ct-K+1]+1);
		}
		Console.WriteLine(ans);
	}
}