while num = gets.split(" ").map(&:to_i) do
  if(num[0] == 0 && num[1] == 0) then
    exit
  end
  for i in 1..num[0] do
    for j in 1..num[1] do
      if (i + j) % 2 == 0 then
        printf "#"
      else
        printf "."
      end
    end
    printf "\n"
  end
  printf "\n"
end