题目描述
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.Between 2 cases you should print a blank line. You may assume the result will be in the range of 32-bit signed integer.