#include <bits/stdc++.h>
using namespace std;
long long Res;
long long n;
void OpenFile() {
  freopen(
      "268B_Buttons"
      ".inp",
      "r", stdin);
  freopen(
      "268B_Buttons"
      ".out",
      "w", stdout);
}
void ReadData() { scanf("%d", &n); }
void SolveProblem() {
  long long Res = n;
  for (long long i = 1; i < n; i++) Res += i * (n - i);
  printf("%lld", Res);
}
int main() {
  ReadData();
  SolveProblem();
}
