Accumulated Sum up to N

Source: Phước Hưng OJ

Version: Phuoc Hung OJ Extended

Problem Statement

Given a nonnegative integer n, compute 1+2+...+n. For n=0, the sum is zero.

Input

One integer n.

Output

Print the sum of integers from 1 through n.

Subtasks

• Subtask 1 (20%): 0 <= n <= 10.
• Subtask 2 (30%): 0 <= n <= 1000.
• Subtask 3 (50%): 0 <= n <= 100000.

Examples

Example 1

Input

3

Output

6

Explanation

Start at zero and add 1, 2, and 3 to obtain 6.

Example 2

Input

0

Output

0

Explanation

The loop does not run, leaving the sum at zero.