<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 Prob171B {
	public static void main(String[] Args) {
		Scanner in = new Scanner(System.in);
		long side = in.nextInt();
		long ans = (side - 1) * side * 6 + 1;
		System.out.println(ans);
	}
}
