[COCI][2006][C2] SJECIŠTA
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Description
Consider a convex polygon with N vertices, with the additional property that no three diagonals intersect in a single point. Find the number of intersections between pairs of diagonals in such a polygon.
The figure below shows one such polygon with 6 vertices.
Note: a polygon is convex if all of its interior angles are less than 180 degrees.
Format
Input
The first and only line of input contains a single integer N, 3 ≤ N ≤ 100.
Output
Output the number of intersections on a single line.
Samples
3
0
4
1
6
15