#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n;
  cin >> n;
  long long temp = n, target = n - 1, cor = 1;
  while (cor < n) {
    long long pos = 1;
    while (pos < target) {
      pos++;
      temp += cor + 1;
    }
    target--;
    cor++;
  }
  temp += (n - 1);
  cout << temp;
  return 0;
}
