2020/10/7 一场牛客训练赛 狂斌网络流2题： https://github.com/YANGRUZHAO/ACM/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/%E6%9C%80%E5%A4%A7%E6%B5%81(poj3281).cpp
