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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_Star {
public static void main(String[] args) {
    Scanner sc= new Scanner(System.in);
    int n=sc.nextInt();
    int p=0;
    for (int i = 1; i <n; i++) {
        p=p+(12*i);
    }
    System.out.println(p+1);
}
}
