eolymp
bolt
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Problems

Chessboard

Chessboard

Time limit 1 second
Memory limit 128 MiB
4.jpg

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 (n10^3).

Output data

Print the sum of integers on white cells.

Examples

Input example #1
4
Output example #1
68
Source 2019 All-Ukrainian Olympiad, Zhitomyr region, ІІ stage