http://acm.bnu.edu.cn/v3/contest_show.php?cid=6626 http://judge.u-aizu.ac.jp/onlinejudge/finder.jsp?volumeNo=23 http://acm-icpc.aitea.net/index.php?2011%2FPractice%2F%E5%A4%8F%E5%90%88%E5%AE%BF%2F%E8%AC%9B%E8%A9%95 C ``It is guaranteed that, for any pair of rooms in the office, there exists exactly ……