loop do
    h, w = gets.split(" ").map(:&to_i)
    break if h == 0 && w == 0

    evenChess = (0...w).map  { |i| i.even? ? "#" : "." }.join
    oddChess = (0...w).map  { |i| i.even? ? "." : "#" }.join

    h.times do |i|
        chess = i.even? ? evenChess : oddChess
        putschess
    end
    puts
end