while true do
    i = gets
    h = i.split[0].to_i
    w = i.split[1].to_i
    break if h == 0 && w == 0
    h.times do |x|
        w.times do |y|
            print "#" if (x%2 == 0 && y%2 == 0) || (x%2 == 1 && y%2 == 1)
            print "." if (x%2 == 0 && y%2 == 1) || (x%2 == 1 && y%2 == 0)
        end
        print "\n"
    end
    print "\n"
end

