<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 B171 {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long N = in.nextInt();
        long answer = 6*N*(N-1)+1;
        System.out.println(answer);
    }

}
