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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 B {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int ans = 1;
        for (int i = 2; i <= a; i++) {
            ans += 12*(i-1);
        }
        System.out.println(ans);
    }

}
