input:
7 2 1 4 2 1 4 3 3 4 4 4 4 3 2 1 1 2 2 3 1 4 4 5 5 6 2 7 CC 4 4 QS 5 1
answer:
8
https://www.luogu.com.cn/blog/Link-Cut-Y/p3313-sdoi2014-lv-xing-ti-xie