描述
Hey, welcome to TOJ(Taizhou 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.
样例输入
1
100
样例输出
1
5050
