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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 sad {
    public static void main(String[] args)
    {
    	Scanner inp=new Scanner(System.in);
    	 int i=1,n,cnt=0,x=1;
        n=inp.nextInt();
      
        for(i=1;i<n;i++)
        {
            cnt=cnt+12*i;
            
        }
        System.out.println(cnt+1);
    // <3  #pn #bff
      }
      
      
    }