<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.*;
public class b{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int s = 1;
		for(int i = 2; i <= n; i++){
			s += 12 * (i-1);
		}
		System.out.println(s);
	}
}

//n** {{1}}
//n** {{2}}
//n** {{3}}
