Note that you must start and finish the pipeline on height $1$ and, also, it's guaranteed that the first and last characters of the input string are equal to 0.

翻译：

注意管道的起点和终点的高度必须为 1，同时数据保证输入字符串的首尾字符均为 0。

没看到这句话卡了一个半小时啊啊啊啊啊