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

public class Solution {

    static long sumOfGroup(int k) {
        long k1=k;
        k1--;
        long g=k1*(k1+1)/(long)2;
        
       g=g+1;
        
        long a=1+(g-1)*2;
        
        //long a = (g%2==0)?(g+1):g;
        //System.out.println(a);
        
        return (k)*(a+(k-1));
        
        
        
        
        
        
        
        
        // Return the sum of the elements of the k'th group.
    }

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