#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
const long long Inf = 1e9 + 5;
const long long MaxN = 1e5 + 5;
const long long Min = -MaxN;
int Debug() {
  cout << "BUG"
       << " ";
}
int main() {
  int n;
  cin >> n;
  int ans = 0;
  for (int i = 1; i <= n - 1; i++) {
    if (n - i == 0) {
      break;
    }
    ans += i * (n - i);
  }
  cout << ans + n;
}
