#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, yes = 0, digit = 1, ans = 0, num, limit;
  cin >> n;
  num = n, limit = n;
  while (digit != limit) {
    ans += (digit * num) - yes;
    digit++, num--, yes++;
  }
  cout << ans + 1 << endl;
  return 0;
}
