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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.Arrays;
import java.util.Scanner;

public class ap02 {

    public static void debug(Object... obs)
    {
        System.out.println(Arrays.deepToString(obs));
    }

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