URI Online Judge | 1921

Guilherme and His Kites

By Gustavo Ribeiro, IFPB - Campina Grande BR Brazil

Timelimit: 1

Guilherme loves kites, kites of different colors, forms and sizes. He realized that in order to kites become stable, and thus fly higher, they must have a taut string connecting all pairs of non-neighboors tips.

Despite being a very creative and clever child, Guilherme doesn’t know how to determine the number of strings necessary to make a kite of n sides stable. Could you help him?

Input

The single line of the input contains an integer 3 ≤ n ≤ 105, the number of sides of the kite.

Output

Print a single number, the number of strings that Guilherme needs to make a kite of n sides stable.

Input Samples Output Samples

4

2

10

35

11

44