loop do
  h, w = gets.split.map(&:to_i)
  break if h == 0 && w == 0
  line = "#." * (w / 2 + 1)

  toggle = true
  h.times do |i|
    puts line[0, w] if toggle
    puts line[1, w] if !toggle
    toggle = !toggle
  end
  puts
end