<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 ProblemB {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        long sum = 1;
        for(int i = 1; i < a; i++){
            sum += 12*i;
        }
        System.out.println(sum);
    }

}