until (a = gets.split.map(&:to_i)) == [0,0]
  a[0].times do |i|
    if (i % 2) == 0
      a[1].times do |j|
        if (j % 2) == 0
          print "#"
        elsif
          print "."
        end
      end
      puts
    elsif
      a[1].times do |j|
        if (j % 2) == 0
          print "."
        elsif
          print "#"
        end
      end
      puts
    end
  end
puts
end