base' = cycle "#."
base  = [base'] ++ [tail base'] ++ base

chessBoard [h,w] = unlines $ take h $ map (take w) base

main = do
  s <- getLine
  let [h,w] = map read $ words s

  if [h,w] == [0,0] then return ()
  else do
    putStrLn $ chessBoard [h,w]
    main