In this problem, your task is to calculate SUM(n) = 1 + 2 + 3 + ... + n
The input will consist of a series of integers n, 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。。。。
Sample Input
1
100
Sample Output
1

5050