import java.util.Scanner;
class Program2{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);

		System.out.print("Enter the value of n(1-20): ");
		int n = sc.nextInt();

		if(n >= 1 && n <= 20){
			long term = 1;
			long sum = term;
			for(int i = 2; i <= n; i++){
				term = term + i;
				sum += term;
			}
			System.out.println("The sum is " + sum);
		}
		else{
			System.out.println("Value of n not within range");
		}
	}
}