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: H, W = [int(thing) for thing in list(str(input()).split(" "))]
  banmen_list = []
  for h in range(H):
      banmen_list.append(list(str(input())))
  
  
  def sousa(banmen, kaisu):
      rbanmen_list = banmen
      T = False
      for i in range(H):
          for j in range(W):
              if banmen[i][j] == "#":
                  osen = [(i - 1, j), (i, j - 1), (i, j + 1), (i + 1, j)]
                  for y, x in osen:
                      if x < 0 or y < 0:
                          continue
                      if x > H - 1 or y > W - 1:
                          continue
                      if rbanmen_list[x][y] == "#":
                          continue
                      if banmen[x][y] == "#":
                          continue
                      rbanmen_list[x][y] = "#"
                      T = True
      if T == False:
          if kaisu == 0:
              print(kaisu)
          else:
              print(kaisu + 1)
          return
      else:
          kaisu = kaisu + 1
          sousa(rbanmen_list, kaisu)
  
  
  sousa(banmen_list, 0)
  
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"}]