Number of Triplets
Description
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.
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 xi, yi ( - 1000 ≤ xi, yi ≤ 1000).
It is guaranteed that all given points are different.
Print the single number — the answer to the problem.
Input
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 xi, yi ( - 1000 ≤ xi, yi ≤ 1000).
It is guaranteed that all given points are different.
Output
Print the single number — the answer to the problem.
3<br>1 1<br>2 2<br>3 3<br>
3<br>0 0<br>-1 0<br>0 1<br>
1<br>
0<br>