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


