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

public class Solution {

    static long sumOfGroup(int k) {
        
    int i,j,count=0;
       
        long p= ( (k-1)*(long)(k))/2;
        
        long a= 1+ ( p-1)*2;
       // System.out.println(a);
        
        
       long s=  ((long) (k)* (long)(2* (a+2)  + (k-1)*2  ))/2;
    
        return s;
    }

    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();
    }
}