Number of Parallelograms

Description:

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 (x_i, y_i) (0 ≤ x_i, y_i ≤ 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.

Sample Input:

4
0 1
1 0
1 1
2 0

Sample Output:

1