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: # 15chess
  H, W = (int(i) for i in input().split())
  while H != 0 or W != 0:
      S = "."
      for i in range(H):
          if S[0] == "#":
              S = "."
          else:
              S = "#"
          for i in range(W - 1):
              if S[-1] == "#":
                  S += "."
              else:
                  S += "#"
          print(S, end="")
      print("\n")
      H, W = (int(i) for i in input().split())
  
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    #"}]