Sum One Through N with While

Source: Phước Hưng OJ

Version: Phuoc Hung OJ Extended

Problem Statement

Given nonnegative n, compute 1+2+...+n using while with a separate loop counter and sum accumulator. The empty sum for n=0 is zero.

Input

One integer n.

Output

Print the integer sum from 1 to n.

Subtasks

• Subtask 1 (20%): 0 <= n <= 5.
• Subtask 2 (30%): 0 <= n <= 1000.
• Subtask 3 (50%): 0 <= n <= 100000.

Examples

Example 1

Input

4

Output

10

Explanation

Adding 1,2,3,4 to the initial zero yields 10.

Example 2

Input

0

Output

0

Explanation

With n=0, the loop does not execute.