### Sum Problem

Time Limit: 500 ms Memory Limit: 32768 KiB

#### Problem 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

sdut