Problem Description
Hey, welcome to HDOJ(Hangzhou Dianzi University Online Judge).

In this problem, your task is to calculate SUM(n) = 1 + 2 + 3 + ... + n.
 

Input
The input will consist of a series of integers n, one integer per line.
 

Output
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
 

要解決這樣的問題，首先想到的就是遞迴

int SumN(int n){
if(n == 1){
	return n;
}
else{
	return n +　SumN(n - 1);
}
}