def draw_chessboard(w, h)
  h.times do |i|
    s = "#." * ((w + 2) / 2)
    puts s[i % 2, w]
  end
end

while line = gets.chomp
  break if line == "0 0"
  h, w = line.split(" ").map(&:to_i)
  draw_chessboard(w, h)
  puts
end