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

public class Solution {

    static long sumOfGroup(long k) {
        // Return the sum of the elements of the k'th group.
        
        long a=k*(k-1);
        a=a/2;
        a=(2*a)-1;
        a+=2;
        
        a= (k*a)+ ((((k-1)*k)/2)*2); 
        return a;
        
    }

    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();
    }
}