#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  while (scanf("%d", &n) != EOF) {
    int sum = 0, k = 0;
    for (int i = n; i >= 1; i--) {
      sum += i;
      sum += (i - 1) * k;
      k++;
    }
    printf("%d\n", sum);
  }
  return 0;
}
