#include <bits/stdc++.h>
using namespace std;
bool comp(int a, int b) { return a > b; }
int arr[int(2e5) + 1];
int main() {
  ios_base::sync_with_stdio(false);
  long long n, a, b, c = 0, sum = 0;
  cin >> n;
  sum += n;
  for (int i = 1; i < n; i++) sum += (n - i) * i;
  cout << sum;
}
