Hey, welcome toPDSU OJPingdingshan University Online Judge). In this problem, your task is to calculate SUM(n) = 1 + 2 + 3 + ... + n.

The input will consist of a series of integers n, and n>=0,end of file EOF,one integer per line.

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. 

付高磊