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 = [int(_c) for _c in input().split(" ")]
  S = input()
  
  
  def cal(_S):
      cum = [0]
      flg = False
      cur_zero = 0
      cur_one = 0
      for i, s in enumerate(_S):
          if s == "0":
              if flg:
                  cum.append(cum[-1] + cur_zero + cur_one)
                  flg = False
                  cur_zero = 0
                  cur_one = 0
              cur_zero += 1
          else:
              if cur_zero != 0:
                  flg = True
              cur_one += 1
  
      cum.append(cum[-1] + cur_zero + cur_one)
      return cum
  
  
  def main():
      cum_l = cal(S)
      cum_r = cal(S[::-1])
  
      if K - 1 > len(cum_l):
          print(len(S))
      else:
          longest = 0
          for i in range(len(cum_l) - K):
              total = cum_l[i + K] - cum_l[i]
              if total > longest:
                  longest = total
          for i in range(len(cum_r) - K):
              total = cum_r[i + K] - cum_r[i]
              if total > longest:
                  longest = total
  
          print(longest)
  
  
  main()
  
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."}]