import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	long n = sc.nextInt();
    	if (n == 1) {
    	    System.out.println(0);
    	    return;
    	}
    	long left = 1;
    	long right = n;
    	long total = n;
    	while (right - left > 1) {
    	    total += left * (right - 1);
    	    total += (left + 1) * right;
    	    right--;
    	    left++;
    	}
    	if (right - left == 1) {
    	    total += right * left;
    	}
    	System.out.println(total);
	}
}