Problem Description

Consider a convex polygon with $n$ vertices, and no three (or more) diagonals of this polygon intersect at the same point.

Now, compute the number of intersection points of the diagonals of such a polygon.

Input Format

Input one integer $n$ in a single line.

Output Format

Output one integer in a single line, representing the answer.

3

0

4

1

6

15

Hint

Explanation for Sample 3

Constraints

For all testdata, it is guaranteed that $3 \leq n \leq 100$.

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