The key to this problem is how to find the law and get the favorable figures first. Let's analyze first, under what circumstances, the opponent must lose. Speaking of 2-4 goals, as long as we have 1 ball left, the opponent will lose. Then, how can we make the opponent just take 2-4 balls, so it can only be 5, because in 5 cases, regardless of whether the opponent takes any of 1-3, how can we make the opponent just touch the remaining 5, as long as he touches 6-8? Obviously, as soon as the opponent hits 9, we can only hit 6-8. Similarly, when the opponent encounters 13, 17 ..., as long as the opponent encounters 4n+ 1 (n is a natural number), the opponent loses.

Back to this topic, when A takes three, there is still 13 1, and B only needs two to win. 13 1-2= 129=4*32+ 1。