Sum Problem

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.
样例
样例输入 #1
1
100
样例输出 #1
1

5050
HDOJ-1001
题目来源:HDOJ-1001
时间限制:500 MS
内存限制:32768 KB
Java 类名:Main
64 位整数占位符:%I64d