406575: GYM102443 F Isosceles triangles

You are given a regular polygon with $$$n$$$ vertices. You should find the number of isosceles triangles with vertices that are the vertices of the polygon.

The only line of input contains one integer $$$n$$$ — the number of vertices of a regular polygon ($$$3 \le n \le 10^9$$$).

The output line should contain a single integer — the number of isosceles triangles with vertices that are the vertices of the polygon.

3

1

5

10

An isosceles triangle is a triangle that has at least two equal sides.