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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 b {

	/**
	 * @param args
	 */
	static Scanner in=new Scanner(System.in);
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int n=in.nextInt();
		int ans=1;
		for(int i=1;i<n;i++){
			ans+=6*(2*i);
		}
		System.out.println(ans);
	}

}
