Solution: Whoever reports 19 first will win. You can only quote 1 or 2 at a time, so you can know who can quote 16, 13,/kloc-0, 7, 4, 1, and whoever wins, that is, just quote a multiple of 3+1. So, we can know who reports first, and who wins. No matter what the other party reports, it always reports multiples of 3+1. Finally, it is certain that whoever reports first can report to 19, that is, the other party reports to 20.