output_description: Print the maximum possible number of consecutive people standing on hands
  after at most K directions.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N K
      S
attempt: N, K = list(map(int, input().split()))
  S = input()
  
  ans = -1    # 十分に小さい値
  if (S[0] == '0'):
      stand = 1
  else:
      stand = 0
  
  l = 0
  r = 0
  
  # 尺取り法
  while (r < N):
      # 右端を進めることが可能（進めたときの積がK以下）なら、右端を進める
      if (stand <= K):
          ans = max(ans, r - l + 1)
          if (S[r] == '1' and S[r + 1] == '0'):
              stand += 1
          r += 1
      # 進められない場合、左端と右端が同じなら両者を進める
      # 左端が右端を追い越さないための処理
      elif (l == r):
          l += 1
          r += 1
      # それ以外は左端のみを進める
      else:
          if S[l] == '0' and if S[l + 1] == '1':
              stand -= 1
          l += 1
  
problem_description: 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.
samples: [{"input": "5 1\n    00010", "output": "4\n    \n\nWe can have four consecutive people standing on hands, which is the maximum\nresult, by giving the following direction:\n\n  * Give the direction with l = 1, r = 3, which flips the first, second and third persons from the left.\n\n* * *"}, {"input": "14 2\n    11101010110011", "output": "8\n    \n\n* * *"}, {"input": "1 1\n    1", "output": "1\n    \n\nNo directions are necessary."}]