until (h,w = gets.chomp.split.map(&:to_i)) == [0, 0]
  h.times do |i|
    if i % 2 == 0
      w.times do |j|
        print "#" if j % 2 == 0
        print "." if j % 2 == 1
      end
    else
      w.times do |j|
        print "#" if j % 2 == 1
        print "." if j % 2 == 0
      end
    end
    puts
  end
  puts
end