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 startElement=0;
       long increment=2;
       long sum=0;
        if(k==1){
        	return 1;	
        }
        else if(k>1){
        	startElement=(k*(k-1))+1;
        	sum=startElement;
        }
        
        for(long x=0;x<k-1;x++){
        	startElement +=increment;
        	sum+=startElement;
        }
    	
        return sum;    }

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