class Solver
  def initialize

    loop do
      h, w = gets.chomp.split(' ').map(&:to_i)

      break if h.zero? && w.zero?

      first = ('#.' * w)[0..w-1]
      second = ('.#' * w)[0..w-1]

      h.times do |i|
        puts i.even? ? first : second
      end

      puts 
    end
  end
end

Solver.new