<image>

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.io.*;
   import java.util.*;
   import java.math.*;
  public class star {
      public static void main (String [] args) throws Exception {
         Scanner sc = new Scanner(System.in);
         int l = Integer.parseInt(sc.nextLine());
            long sum = 1;
            sum+=6*(l)*(l+1);
            sum-=12*(l);
            System.out.println(sum);
      }
   }