#include<bits/stdc++.h>
using namespace std;
 
int main() {
    int n;
    cin >> n;
    int sum = 0, a = 1, diff = 1;
    for (int i = 1; i <= n; ++i) {
        sum += a;
        a += diff;
        diff++;
    }
    cout << sum << endl;
}
/**************************************************************
	Problem: 1145
	User: wengsihan
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/