#include <bits/stdc++.h>
int main() {
  int i, j, k, num[10] = {}, n;
  double sum = 2;
  double count = 1, plus;
  while (scanf("%d", &n) != EOF) {
    sum = 2;
    count = 1;
    plus = 1;
    for (i = 0; i < n; i++) {
      plus += sum;
      count += plus;
      sum++;
    }
    printf("%.0f\n", count);
  }
  return 0;
}
