<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 Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int f = scan.nextInt();
        long ans = 0;
        for (; f > 1; f--) {
            ans += (f - 1) * 12;
        }

        System.out.println(ans + 1);

    }
}
