#17330: c++遞迴解法
d10730416@gapps.fg.tp.edu.tw
(Wendy Charng)
#include <iostream>
using namespace std;
int n, A(int);
int main() {
while (cin >> n){
cout << A(n) << endl;
}
}
int A(int n){
if (n == 1) return 1;
else return A(n - 1) + n - 1;
}