#include <bits/stdc++.h>
int main(void) {
  unsigned long long cnt;
  int n, i;
  while (scanf("%d", &n) != EOF) {
    cnt = 0;
    for (i = 1; i < n; i++) {
      cnt += (i * i + 5 * i + 6) / 2;
    }
    printf("%lld\n", cnt + 4);
  }
  return 0;
}
