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: Accepted)

from collections import deque

N, K = [int(a) for a in input().split()]
S = input()

L = deque()

n_zero = 0  # 通過した0の塊の数
r = 0 # 連続する0の塊がK個含まれるSの連続部分列の右端の位置
l = 0
# rの値を探す
while r < N and n_zero < K:
    if S[r] == "0": n_zero += 1
    while r < N and S[r] == "0":
        r += 1
    if 0 < r < N and S[r] == "1":
        L.append(r)
    while r < N and S[r] == "1":
        r += 1

ans = r

while len(L) > 0 and r < N:
    l = L.popleft()
    while r < N and S[r] == "0":
        r += 1
    if r < N and S[r] == "1":
        L.append(r)
    while r < N and S[r] == "1":
        r += 1
    ans = max(ans, r - l)

print(ans)