#include <iostream>

using namespace std;

static void setup()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
}

int main(int argc, char **argv)
{
    setup();
    int n;
    cin >> n;

    auto sum = 0;
    for (auto i = 1; i <= n; ++i) {
        sum += i;
    }

    cout << sum << endl;
    return 0;
}