# 2002-2003 ACM Northeastern European Regional Programming Contest

## Practice Session - Problem S
"Sum"

Input file: | `sum.in`
Output file: | `sum.out`

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

### Input

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

### Output

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

### Sample inputs and outputs

sum.in | sum.out
    2
    3
    -3
    -5