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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.*;
 
public class Main {
    public static void main(String[] args) 
    {
 
    Scanner sc = new Scanner(System.in);
     long n = sc.nextLong();
 
      System.out.print(6 * n * (n - 1) + 1);
 
    }
}