ARGF.each_line do |line|
  h, w = line.split.map(&:to_i)
  break if (h == 0) && (w == 0)
  i = 0
  loop do
    i += 1
    break if i > h
      if i.odd?
        w.times{|n| print n.odd? ? "." : "#"}
        puts
      else
        w.times{|n| print n.odd? ? "#" : "."}
        puts
      end
    end
end