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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 B171 {

	public static void main(String[] args)
	{
		Scanner read = new Scanner(System.in);
		short input = read.nextShort();
		read.close();
		System.out.println((6*input*(input-1))+1);
	}
}
