Counting Intersection Points of Diagonals in a Convex Polygon

Given a convex polygon with n vertices, where no three or more diagonals intersect at a single point, determine the number of intersection points produced by the diagonals. The answer can be derived from the formula:

$$ \binom{n}{4} = \frac{n \times (n-1) \times (n-2) \times (n-3)}{24} $$

Note that if n < 4, no intersection is possible, and the output should be 0.

inputFormat

The input consists of a single integer n representing the number of vertices of the convex polygon.

outputFormat

Output a single integer which is the number of intersection points among the diagonals of the convex polygon.

sample

3

0