1006 Sum Problem

题目描述

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

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

输入

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

输出

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.

示例输入

1100

示例输出

15050

来源

sdut