## Description:

Hey, welcome to HDOJ(Hangzhou Dianzi University Online Judge).

In this problem, your task is to calculate SUM(n) = 1 + 2 + 3 + ... + n.

## Input:

The input will consist of a series of integers n, one integer per line.

## Output:

For each case, output SUM(n) in one line, followed by a blank line. You may assume the result will be in the range of 32-bit signed integer.

## Sample Input:

1
100

## Sample Output:

1
5050