题目描述
You are given a tree consisting of $n$ vertices, and $m$ simple vertex paths. Your task is to find how many pairs of those paths intersect at exactly one vertex. More formally you have to find the number of pairs $(i, j)$ $(1 \leq i < j \leq m)$ such that $path_i$ and $path_j$ have exactly one vertex in common.
Input
First line contains a single integer $n$ $(1 \leq n \leq 3 \cdot 10^5)$.
Next $n - 1$ lines describe the tree. Each line contains two integers $u$ and $v$ $(1 \leq u, v \leq n)$ describing an edge between vertices $u$ and $v$.
Next line contains a single integer $m$ $(1 \leq m \leq 3 \cdot 10^5)$.
Next $m$ lines describe paths. Each line describes a path by it's two endpoints $u$ and $v$ $(1 \leq u, v \leq n)$. The given path is all the vertices on the shortest path from $u$ to $v$ (including $u$ and $v$).
Output
Output a single integer — the number of pairs of paths that intersect at exactly one vertex.
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分
样例输入
样例输出
提示
The tree in the first example and paths look like this. Pairs $(1,4)$ and $(3,4)$ intersect at one vertex.
In the second example all three paths contain the same single vertex, so all pairs $(1, 2)$, $(1, 3)$ and $(2, 3)$ intersect at one vertex.
The third example is the same as the first example with two additional paths. Pairs $(1,4)$, $(1,5)$, $(2,5)$, $(3,4)$, $(3,5)$, $(3,6)$ and $(5,6)$ intersect at one vertex.