P7540 [COCI 2009/2010 #1] DOMINO

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

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

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

#### 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**](https://hsin.hr/coci/archive/2009_2010/contest1_tasks.pdf) _**T2 DOMINO**_. Translated by ChatGPT 5