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