#include <bits/stdc++.h>
using namespace std;
long long ret(long long n) {
  n--;
  long long a = ((n * (n + 1)) / 2 + 1);
  return a;
}
int main() {
  long long n;
  cin >> n;
  long long sum = 0;
  for (long long i = 1; i <= n; i++) {
    sum += (ret(i));
  }
  cout << sum;
}
