这是ACM的一道试题.内容是:“蛇和梯子”是一个在N*N（0<N<=20)的方格棋盘上进行的游戏.-This is a test of the ACM. It reads : "snakes and ladders" is one of the N * N (0lt; Nlt; = 20) in the box on the chessboard of the game.