#include <iostream>
using namespace std;
int main() {
long long x;
cin>>x;
long long sum = x * (x + 1) / 2;
cout << sum;
}
I2luY2x1ZGUgPGlvc3RyZWFtPgp1c2luZyBuYW1lc3BhY2Ugc3RkOwoKaW50IG1haW4oKSB7CiAgCiAgbG9uZyBsb25nIHg7CiAgY2luPj54OwogIGxvbmcgbG9uZyBzdW0gPSB4ICogKHggKyAxKSAvIDI7CiAgY291dCA8PCBzdW07Cn0K