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: Time Limit Exceeded)

import re

N, K = list(map(int, input().split()))
S = input()
intS = int(S, 2)

def popcnt(n):
  return bin(n).count("1")

cands = []
for xor in range(2 ** len(S)):
  if len(re.split('1+', bin(xor))) != 2:
    continue
  cands.append(xor)

for _ in range(K):
  best_score = max([len(v) for v in re.findall(r'1+', S)])
  best_xor = 0
  for xor in cands:
    res = intS ^ xor
    try:
      score = max([len(v) for v in re.findall(r'1+', bin(res))])
    except:
      score = 0
    
    if score > best_score:
      best_score = score
      best_xor = xor
      # print(xor, bin(xor), res, bin(res), _popcnt)
        
  intS = intS ^ best_xor
    
print(max([len(v) for v in re.findall(r'1+', bin(intS))]))