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