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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 Main {
    static long sol;
    static int a;

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