Number of Triplets
题目描述
B. Number of Triplets
time limit per test
2 secondsmemory limit per test
256 megabytesinput
standard inputoutput
standard outputYou 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.
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.
Examples
Input
3
1 1
2 2
3 3
Output
1
Input
3
0 0
-1 0
0 1
Output
0
题目来源：fps-www.educg.net-codeforce-1-2833.xml.zip；FPS 共享题包，题包内第 2511 题。保留原作者与原赛事署名。