while (h, w = gets.split(" ").map(&:to_i)) != [0,0]
  h.times do |n|
    if n.even?
        puts Array.new((w+1)/2,["#","."]).flatten[0..w-1].join("")
    else
        puts Array.new((w+1)/2,[".","#"]).flatten[0..w-1].join("")
    end
  end
  puts "\n"
end

