#include <iostream>
using namespace std;

int main() {

    int n;
    cin >> n;
    int pocetok = 1;
    int kraj = n;
    int zbir = 0;
    while(pocetok <= kraj) {
        zbir += pocetok;
        pocetok += 1;
    }
    cout << zbir << endl;

    return 0;
}