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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 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt();
        long res = 1;
        long x = 12;
        for (int i = 1 ; i < a; i++){
            res += x;
            x+=12;
        }
        System.out.println(res);

    }

}
