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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;

/**
 *
 * @author owner
 */
public class JavaApplication7 {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        int n = (new Scanner(System.in)).nextInt();
        System.out.print(6*n*(n-1)+1);
        
    }
}
