Lyestria is observing a group of ~N~ frogs. The frogs are numbered from ~1~ to ~N~.
The frog numbered ~i~ conveniently lives at the point ~i~. On this day, the frog numbered ~i~ wants to go to the point ~N-i+1~, where all the points are equally spaced.
Lyestria then asks you to compute the sum of the distances each frog must travel to get to their desired location.
~1 \le N \le 10^9~
The first line contains one integer, ~N~, the number of frogs.
On one line, output one integer, the sum of the distances each frog must travel to get home.
Sample Input 2
Sample Output 2