#include <bits/stdc++.h>
using namespace std;
const int M = 10000000;
int a[M];
int num[M];
int main() {
  int n;
  cin >> n;
  int res = n;
  for (int i = n - 1; i > 0; i--) {
    res += i * (n - i);
  }
  cout << res << '\n';
  return 0;
}
