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A8492 | $Number of Triplets$

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题目描述

You are given $n$ points on a plane. All points are different. Find the number of different groups of three points $(A,B,C)$ such that point $B$ is the middle of segment $AC$ . The groups of three points are considered unordered, that is, if point $B$ is the middle of segment $AC$ , then groups $(A,B,C)$ and $(C,B,A)$ are considered the same.

输入格式

The first line contains a single integer $n$ ( $3<=n<=3000$ ) — the number of points. Next $n$ lines contain the points. The $i$ -th line contains coordinates of the $i$ -th point: two space-separated integers $x_{i},y_{i}$ ( $-1000<=x_{i},y_{i}<=1000$ ). It is guaranteed that all given points are different.

输出格式

Print the single number — the answer to the problem.

输入输出样例

输入 #1

输出 #1

输入 #2

输出 #2

C++ 编辑器

输入

输出