Could anybody give me any hint?
(I know algoritm with O(n^4), but I always receive Time Limit
Exceeded.)E-mail me to vok@sbor.ru

Thanks!

Facts:
 1.You must find the minimal ring
 2.Traveling in DFS let you see rings
 3. The minimum ring is related to the minimum distance
In fact this is a just a minimum distance problem, which can be
solved in O(n log n), but with a fast algorithm in O(n^2).
Doubts: miguelangelhdz@hotmail.com