while true
    numbers = gets.split.map(&:to_i)
    if numbers[0] == 0 && numbers[1] == 0
        break
    else
        (numbers[0]).times do |num_r|
            st = ""
            (numbers[1]).times do |num_c|
                if num_r %2 ==0
                    if num_c %2 ==0
                        st+= "#"
                    else
                        st+= "."
                    end
                else
                    if num_c %2 ==0
                        st+= "."
                    else
                        st+= "#"
                    end
                end
            end
            puts st
        end
    end
    puts ""
end
