Vera's Fashion

Vera owns $N$ tops and $N$ bottoms. The $i$-th top and the $i$-th bottom both have color $i$. The $N$ colors are all different.

Vera picks one top and one bottom. How many such pairs have a top and a bottom of different colors?

The input is given in the following form.

N

Print the number of pairs whose top and bottom have different colors, on one line.

• $1 \le N \le 2017$
• $N$ is an integer.