output_description: For each dataset, print the chessboard made of '#' and '.'.
  
  Print a blank line after each dataset.
input_description: The input consists of multiple datasets. Each dataset consists of two integers
  H and W separated by a single space.
  
  The input ends with two 0 (when both H and W are zero).
attempt: c = []
  
  
  def listcreate():
      global c
      c = []
      for y in range(a[0]):
          b = []
          for x in range(a[1]):
              if (x + y) % 2 == 0:
                  b.append("#")
              else:
                  b.append(".")
          c.append(b)
      return
  
  
  def listdraw():
      global c
      for y in range(len(c)):
          for x in range(len(c[0])):
              print(c[y][x], end="")
          print()
      return
  
  
  for i in range(10000):
      a = list(map(int, input().split()))
      if sum(a) == 0:
          break
      listcreate()
      listdraw()
      print()
  
problem_description: Print a Chessboard
  
  Draw a chessboard which has a height of H cm and a width of W cm. For example,
  the following figure shows a chessboard which has a height of 6 cm and a width
  of 10 cm.
  
      
      
      #.#.#.#.#.
      .#.#.#.#.#
      #.#.#.#.#.
      .#.#.#.#.#
      #.#.#.#.#.
      .#.#.#.#.#
      
  
  Note that the top left corner should be drawn by '#'.
samples: [{"input": "4\n    5 6\n    3 3\n    2 2\n    1 1\n    0 0", "output": "#.#.\n    .#.#\n    #.#.\n    \n    #.#.#.\n    .#.#.#\n    #.#.#.\n    .#.#.#\n    #.#.#.\n    \n    #.#\n    .#.\n    #.#\n    \n    #.\n    .#\n    \n    #"}]