CF181B.Number of Triplets

普及/提高-

通过率：0%

AC君温馨提醒

该题目为【codeforces】题库的题目，您提交的代码将被提交至codeforces进行远程评测，并由ACGO抓取测评结果后进行展示。由于远程测评的测评机由其他平台提供，我们无法保证该服务的稳定性，若提交后无反应，请等待一段时间后再进行重试。

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
```
3
1 1
2 2
3 3
```
输出#1
```
1
```
输入#2
```
3
0 0
-1 0
0 1
```
输出#2
```
0
```

首页