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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 {

	
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int num = in.nextInt();
		
		int sum = (num-1)*(num) / 2;
		System.out.println(12*sum + 1);
	}
}
