#include <iostream>
#include <vector>
#include <algorithm>

#define REP(i, a, b) for (int i = int(a); i < int(b); i++)

using namespace std;

typedef long long int lli;

int main() {
    int N;
    cin >> N;
    cout << N * (N + 1) / 2 << endl;
    return 0;
}