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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 Stars {
	public static void main (String [] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int starSequence = 6*n *(n-1) + 1;
		System.out.println(starSequence);
	}
}
