Sjecišta
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. 
Inputhe first and only line of input contains a single integer N, 3 ≤ N ≤ 100.
OutputOutput the number of intersections on a single line.
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3 Output
0Input
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4 Output
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