A13437 | Journey

In the wilds far beyond lies the Land of Sacredness, which can be viewed as a tree — connected undirected graph consisting of $n$ nodes and $n-1$ edges. The nodes are numbered from $1$ to $n$ .

There are $m$ travelers attracted by its prosperity and beauty. Thereupon, they set off their journey on this land. The $i$ -th traveler will travel along the shortest path from $s_i$ to $t_i$ . In doing so, they will go through all edges in the shortest path from $s_i$ to $t_i$ , which is unique in the tree.

During their journey, the travelers will acquaint themselves with the others. Some may even become friends. To be specific, the $i$ -th traveler and the $j$ -th traveler will become friends if and only if there are at least $k$ edges that both the $i$ -th traveler and the $j$ -th traveler will go through.

Your task is to find out the number of pairs of travelers $(i, j)$ satisfying the following conditions:

- $1 \leq i < j \leq m$ .
- the $i$ -th traveler and the $j$ -th traveler will become friends.

The first line contains three integers $n$ , $m$ and $k$ ( $2 \le n, m \le 1.5 \cdot 10^5$ , $1\le k\le n$ ).

Each of the next $n-1$ lines contains two integers $u$ and $v$ ( $1 \le u,v \le n$ ), denoting there is an edge between $u$ and $v$ .

The $i$ -th line of the next $m$ lines contains two integers $s_i$ and $t_i$ ( $1\le s_i,t_i\le n$ , $s_i \neq t_i$ ), denoting the starting point and the destination of $i$ -th traveler.

It is guaranteed that the given edges form a tree.

The only line contains a single integer — the number of pairs of travelers satisfying the given conditions.