while true do
    h,w = gets.split.map(&:to_i)
    break if h ==0 && w ==0
    h.times do |i|
        str = ''
        if i%2 == 0 then
            w.times do |j|
                if j%2 == 0 then
                    str+='#'
                else
                    str+='.'
                end
            end
        else
            w.times do |j|
                if j%2 == 0 then
                    str+='.'
                else
                    str+='#'
                end
            end
        end
        puts str
    end
    puts
end
