John got a bad mark in math. The teacher gave him another task. John is to write a program which computes the sum of integers from $1$ to $n$. If he manages to present a correct program, the bad mark will be cancelled.
Write a program which:
- reads the number $n$ from the standard input,
- computes the sum of integers from $1$ to $n$,
- writes the answer to the standard output.
Input Format
The first and only line of the standard input contains one integer $n$ ($1 ≤ n ≤ 10\,000$).
Output Format
One integer is to be written to the standard output. This integer should be the sum of integers from $1$ to $n$.
Example
Input
3
Output
6