Description

For all non-negative integer pairs $(x, y)$ that satisfy $0 \le x \le y \le N$, find the value of $\sum{x} + \sum{y}$.

Input Format

One line with one integer $N$, as described in the statement.

Output Format

One line with one integer, representing the value of $\sum{x} + \sum{y}$.

2

12

3

30

15

2040

Hint

Sample 2 Explanation

All pairs that satisfy the requirement are: $(0,0)$, $(0,1)$, $(0,2)$, $(0,3)$, $(1,1)$, $(1,2)$, $(1,3)$, $(2,2)$, $(2,3)$, $(3,3)$.

Constraints

For $100\%$ of the testdata, $1 \le n \le 10^3$.

Notes

The scoring of this problem follows the original COCI problem settings, with a full score of $50$.

Translated from COCI2009-2010 CONTEST #1 T2 DOMINO.

Translated by ChatGPT 5