input：
2 1 2
output：
0
即无解情况。
hacked:
https://www.luogu.com.cn/article/xoebz9lm
https://www.luogu.com.cn/article/9zknyfxy
https://www.luogu.com.cn/article/z524e5xj
https://www.luogu.com.cn/article/oafiygi0
https://www.luogu.com.cn/article/fcytdw4p
https://www.luogu.com.cn/article/c670f0hs
细节问题，建议加个注释，应该不用撤下。
