A. Vera and Outfits
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output

Vera owns N tops and N pants. The i-th top and i-th pants have colour i, for 1 ≤ i ≤ N, where all N colors are different from each other.

An outfit consists of one top and one pants. Vera likes outfits where the top and pants are not the same colour.

How many different outfits does she like?

Constraints:

1 ≤ N ≤ 2017

N is integer

Input

The input will be in the format:

N

Output

Output one line with the number of different outfits Vera likes.

Examples
Input
1
Output
0
Input
2
Output
2
Input
5
Output
20