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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 input = new Scanner(System.in);
		int a = input.nextInt();
		System.out.println((a * (a - 1) * 6) + 1);

	}

}
