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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 star {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextLong();
		long ans = 0;
		for(int a=1;a<N;a++){
			ans+=a;
		}
		System.out.println(((ans*6)<<1)+1);
		
	}

}
