Sum from 1 to N

Source: Phước Hưng OJ

Version: Phuoc Hung OJ Extended

Problem Statement

Given nonnegative n, compute 1+2+...+n. For n=0 the sum is zero. Practice accumulation in a for loop and signed 64-bit arithmetic.

Input

One integer n.

Output

One integer representing the sum.

Subtasks

• Subtask 1 (20%): $0\le n\le10$.
• Subtask 2 (30%): $0\le n\le10^4$.
• Subtask 3 (50%): $0\le n\le10^7$.

Examples

Example 1

Input

5

Output

15

Explanation

0+1+2+3+4+5=15.

Example 2

Input

0

Output

0

Explanation

The loop runs zero times, leaving the sum at zero.