Number of Parallelograms
题目描述
D. Number of Parallelograms
time limit per test
4 secondsmemory limit per test
256 megabytesinput
standard inputoutput
standard outputYou are given n points on a plane. All the points are distinct and no three of them lie on the same line. Find the number of parallelograms with the vertices at the given points.
Input
The first line of the input contains integer n (1≤n≤2000) − the number of points.
Each of the next n lines contains two integers (xi,yi) (0≤xi,yi≤109) − the coordinates of the i-th point.
Output
Print the only integer c − the number of parallelograms with the vertices at the given points.
Example
Input
4
0 1
1 0
1 1
2 0
Output
1
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