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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.io.*;
import java.util.*;
import java.lang.Math.*;
public class star_num
{
     public static void main(String args[])throws Exception
     {
         Scanner in=new Scanner(System.in);
         int n=in.nextInt();
         System.out.println((6*n)*(n-1)+1);
     }
}