Lyestria is observing a group of frogs. The frogs are numbered from to .
The frog numbered conveniently lives at the point . On this day, the frog numbered wants to go to the point , 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.
The first line contains one integer, , 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