链接：JXCPC A-Cotree
Avin has two trees which are not connected. He asks you to add an edge between them to make them connected while minimizing the function ∑ i = 1 n ? 1 ∑ j = i + 1 n d i s t a n c e ( i , j ) \sum_{i=1}^{n-1}\sum_{j=i+1}^{n}distance(i,j) i=1∑n?1?j=i+1∑n?distance(i,j), where dis(i, j) represents the number of edges of the path from i to j. He is happy with only the function value.
Input
The first line contains a number n (2<=n<=100000). In each of the following n?2 lines, there are two numbers u and v, meaning that there is an edge between u and v. The input is guaranteed to contain exactly two trees.
Output
Just print the minimum function value.
Sample Input
3
1 2
Sample Output
4
题意：
给出两棵树（共n个结点，即n-2条边），加一条边连接两棵树使得得到的新树上结点两两距离和最小。即 ∑ i = 1 n ? 1 ∑ j = i