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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 Star {
	private static Scanner in = new Scanner(System.in);
	public static void main(String[] args) {
		int a = in.nextInt();
		int ret = 6*a*a - 6*a + 1;
		System.out.println(ret);
	}
}
