<image>

Input

The input contains a single integer a (1 ≤ a ≤ 18257).

Output

Print a single integer output (1 ≤ output ≤ 2·109).

Examples

Input

2


Output

13

import java.util.Scanner;

public class B {
public static void main(String[] args) {

    Scanner s = new Scanner(System.in);

    long a = s.nextInt();
    
    System.out.println(a * (a - 1) / 2 * 12 + 1);
}
}