#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i, n) for (int i = 1; i <= (n); ++i)

int main() {
    int n, ans = 0;
    cin >> n;
    rep2(i, n) { ans += i; }
    cout << ans << endl;
    return 0;
}