Codeforces Round 177 (Div. 1)
D
Polo the Penguin and Trees
Codeforces
2400
原题
← CE →
翻译中…

Little penguin Polo has got a tree — a non-directed connected acyclic graph, containing $*n*$ nodes and $*n* - 1$ edges. We will consider the tree nodes numbered by integers from 1 to $*n*$.

翻译中…

Today Polo wonders, how to find the number of pairs of paths that don't have common nodes. More formally, he should find the number of groups of four integers $*a*, *b*, *c*$ and $*d*$ such that:

翻译中…
  • $1 ≤ *a* < *b* ≤ *n*$;
  • $1 ≤ *c* < *d* ≤ *n*$;
  • there's no such node that lies on both the shortest path from node $*a*$ to node $*b*$ and from node $*c*$ to node $*d*$.
翻译中…

The shortest path betweem two nodes is the path that is shortest in the number of edges.

翻译中…

Help Polo solve this problem.

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Input

翻译中…

The first line contains integer $*n*$ $(1 ≤ *n* ≤ 80000)$ — the number of tree nodes. Each of the following $*n* - 1$ lines contains a pair of integers $*u*_{*i*}$ and $*v*_{*i*}$ $(1 ≤ *u*_{*i*}, *v*_{*i*} ≤ *n*; *u*_{*i*} ≠ *v*_{*i*})$ — the $*i*$-th edge of the tree.

翻译中…

It is guaranteed that the given graph is a tree.

翻译中…

Output

翻译中…

In a single line print a single integer — the answer to the problem.

翻译中…

Please do not use the %lld specificator to read or write 64-bit numbers in С++. It is recommended to use the cin, cout streams or the %I64d specificator.

翻译中…

样例

Input #1
4
1 2
2 3
3 4
Output #1
2
InputCopy OutputCopy
题目信息
题号
288D
时间限制
2 s
内存限制
256 MB
标签
组合数学
DFS 及类似
树

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