import java.util.Scanner;
public class HelloWorld {
public static void main(String []args) {
Scanner scan = new Scanner(System.in);
System.out.print("n : ");
int n = scan.nextInt();
int subs=0;
int s=0;
for(int i=1; i<=n; i++) {
subs = subs + i;
s = s + subs;
}
System.out.println(s);
}
}