#include <iostream>
using namespace std;

int zbir(int N) {
    int sum = 0;
    for(int i = 1; i <= N; i += 1) {
        sum += i;
    }
    return sum;
}
int main() {
    int n;
    cin >> n;
    cout << zbir(n) << endl;

    return 0;
}