while (h, w = gets.split.map(&:to_i))!=[0,0] do
    h.times do |i|
		if (i%2)==0 then
			print("#."*(w/2))
			puts w%2==0 ? "" : "#"
		else
			print(".#"*(w/2))
			puts w%2==0 ? "" : "."
		end
	end
	puts
end
