UVA925 No more prerequisites, please!

Description

[problemUrl]: https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=11&page=show_problem&problem=866 [PDF](https://uva.onlinejudge.org/external/9/p925.pdf) ![](https://cdn.luogu.com.cn/upload/vjudge_pic/UVA925/071ae5004bf5e54a48170d62053a4ebff5e3452b.png)

Input Format

![](https://cdn.luogu.com.cn/upload/vjudge_pic/UVA925/810a595f34b003f4d5fd612d695a454376410c92.png)

Output Format

![](https://cdn.luogu.com.cn/upload/vjudge_pic/UVA925/d014b7a480dea298fb6c3187c6cb8194092ddc04.png)