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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.*;

public class B
{
	public static void main(String args[])
	{
		Scanner scan = new Scanner(System.in);

		int n = scan.nextInt();
		int rtn = 1;
		for(int i=2;i <= n;i++)
			rtn += (i-1)*12;

		System.out.println(rtn);
	}
}