until(h, w = gets.split.map(&:to_i)) == [0,0]
  h.times do |i|
    if i.even?
      if w.odd?
        puts "#{"#." * (w/2)}#"
      else puts "#{"#." * (w/2)}"
      end
    elsif w.odd?
      puts "#{".#" * (w/2)}."
    else puts "#{".#" * (w/2)}"
    end
  end
    puts ""
end