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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.Scanner;

public class fool1 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n;
		
		n = sc.nextInt();
		
		long val = 1;
		
		n -= 1;
		while(n>0){
			val += 12*n;
			n--;
		}
		
		System.out.println(val);
	}
}
