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 Python (3.4.3) (judge verdict: Wrong Answer)

def main():
    input = sys.stdin.readline
    try:
        N,K = map(int,input().split())
        S = input()
        arr = []
        before = S[0]
        cnt = 0
        for s in S:
            if s == before:
                cnt += 1
            else:
                arr.append(cnt)
                cnt = 1
                before = s
        tmp = sum(arr[:K**2+1])
        result = [tmp]
        for i in range(0, len(arr) - K ** 2 - 1, K):
            tmp += sum(arr[i+(K**2)+1 : i+(K**2)+1+K])
            tmp -= sum(arr[i : i+K])
            result.append(tmp)
        print(max(result))
    finally:
        input = None

import sys; sys.setrecursionlimit(50000)
if __name__ == "__main__":
    main()