Sum from 1 to n (High Precision)

Problem Background

Special for beginners, ^_^

Problem Description

Using high-precision arithmetic, compute the exact value of $s = 1 + 2 + 3 + \dots + n$ ($1 \le n \le 10^6$).

Input Format

An integer $n$.

Output Format

Output the value of $s$.

Sample Input

10

Sample Output

55

Constraints

1s, 1024KiB for each test case.