Your task is to find the sum of all integer numbers
lying between 1 and *N* inclusive.

### Input

The input consists of a single integer *N* that is
not greater than 10000 by it's absolute value.

### Output

Write a single integer number that is the sum of all
integer numbers lying between 1 and *N* inclusive.

### Sample

**Problem Source: **2000-2001 ACM Northeastern European Regional Programming Contest (test tour)