#include <bits/stdc++.h>

using namespace std;

long long solve(int n) {
  if (n == 1)
    return 0;

  long long ret = n;
  for (long long l = 1, r = n; l < r; l++, r--) {
    if (l + 1 == r) {
      ret += l * r;
    } else {
      ret += l * (r - 1);
      ret += (l + 1) * r;
    }
  }
  return ret;
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n;
  cin >> n;
  cout << solve(n) << endl;
  
  return 0;
}