#include <bits/stdc++.h>
using namespace std;
long long int MODULO = 1e9 + 7;
bool myAssert(bool b);
void testDrivenDevelopment();
int start(int argc = 0, char const *argv[] = NULL);
vector<int> *g;
bool *isvisited;
int main(int argc, char const *argv[]) {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  long long int res = 0;
  res = (n + 1) + (n - 2);
  for (int i = 2; i <= (n - 1); i++) {
    res += (i * (n - i));
  }
  cout << res << "\n";
  return 0;
}
