Welcome, heroes

This is an exercise on pull requests. I have a problem that I can't solve and I need your help. The only way I can receive your contributions is via pull requests.

Problem Statement

You are given a positive integer n. Your task is to find the sum of all positive integers less than or equal to n.

Input

The input consists of a single integer n (1 ≤ n ≤ 10⁹).

Output

Print a single integer, the sum of all positive integers less than or equal to n.

Examples

Input: 5

Output: 15

Input: 10

Output: 55

Contribution

1. Fork the repository to your personal account
2. Clone the forked repo into your local machine
3. Create a file with yourname and md extension, like mohamed-elsherbiny.md
4. Write your solution inside the file
5. Commit your changes, push to the remote repository
6. Create a pull request using GitHub website interface

Need help?

See this video if you can't figure out how.