output_description: Print the number of operations that will be performed.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      H W
      A_{11}A_{12}...A_{1W}
      :
      A_{H1}A_{H2}...A_{HW}
attempt: # import copy
  import random
  
  H, W = map(int, input().split())
  # dist_matrix = [[10000] * W for i in range(H)]
  black_h_list = []
  black_w_list = []
  for i in range(H):
      line_list = list(input())
      for j in range(W):
          if line_list[j] == "#":
              black_h_list.append(i)
              black_w_list.append(j)
  
  # print(black_h_list)
  # print(black_w_list)
  
  max_value = 0
  for index in range(1000):
      i = int(random.random() * H)
      j = int(random.random() * W)
      min_dist = H + W + 2
      for k in range(len(black_h_list)):
          dist = abs(i - black_h_list[k]) + abs(j - black_w_list[k])
          if max_value >= dist:
              min_dist = dist
              break
          elif min_dist > dist:
              min_dist = dist
      # dist_matrix[i][j] = min_dist
      if max_value < min_dist:
          max_value = min_dist
  
  # print(dist_matrix)
  
  print(max_value)
  
problem_description: Statement
  
  You are given a grid of squares with H horizontal rows and W vertical columns,
  where each square is painted white or black. HW characters from A_{11} to
  A_{HW} represent the colors of the squares. A_{ij} is `#` if the square at the
  i-th row from the top and the j-th column from the left is black, and A_{ij}
  is `.` if that square is white.
  
  We will repeatedly perform the following operation until all the squares are
  black:
  
    * Every white square that shares a side with a black square, becomes black.
  
  Find the number of operations that will be performed. The initial grid has at
  least one black square.
samples: [{"input": "3 3\n    ...\n    .#.\n    ...", "output": "2\n    \n\nAfter one operation, all but the corners of the grid will be black. After one\nmore operation, all the squares will be black.\n\n* * *"}, {"input": "6 6\n    ..#..#\n    ......\n    #..#..\n    ......\n    .#....\n    ....#.", "output": "3"}]