METODA 1 - CEA A RUXANDREI (EU AM FACUT-O COMPLET, FARA ALTE GRESELI)
#include<iostream>
using namespace std;
int main() {
int n;
cin >> n;
cout << (n * (n + 1)) / 2;
return 0;
}
METODA 2 - ITERATIV - CU FOR
#include<iostream>
using namespace std;
int main() {
int n, s = 0;
cin >> n;
for (int i = 1; i <= n; i++)
s = s + i;
cout << s;
return 0;
}