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