Problems
Chessboard
Chessboard
The cells of the chessboard of size n x n are enumerated with positive integers from 1 to n^2
as shown in the picture. Find the sum of integers on white cells.
Input data
One even positive integer n (n ≤ 10^3
).
Output data
Print the sum of integers on white cells.
Examples
Input example #1
4
Output example #1
68