import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

   static long sumOfGroup(long k) {
	        long before=k*(k-1)+1;
	        long after=k*(k+1)-1;
	        long sum=0;
	     sum=((before+after)/2)*k;
		 
	    return  sum;
	  }

	    public static void main(String[] args) {
	        Scanner in = new Scanner(System.in);
	        long k = in.nextLong();
	        long answer = sumOfGroup(k);
	        System.out.println(answer);
	        in.close();
	    }
	}