#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; ++i)
using ll = long long;
using namespace std;
const int INF = 1e9;

int main() {
    int n;
    cin >> n;

    cout << n * (n + 1) / 2 << endl;

    return 0;
}