#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

ll get_sum(ll n){
    ll m = (n - 1);
    return n + m * (m + 1);
}

long sumOfGroup(ll k) {
    ll n = (k * (k + 1)) / 2;
   return get_sum(n) - get_sum(n - k);
}

int main() {
    ll k;
    cin >> k;
    ll answer = sumOfGroup(k);
    cout << answer << endl;
    return 0;
}