#include <bits/stdc++.h>

using namespace std;

long sumOfGroup(int k) {
    long firstNumberRank = (long(k)*(k-1))/2;
    return(k*(2*firstNumberRank+k));
}

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