import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan=new Scanner(System.in);
		int A=scan.nextInt();
		int B=scan.nextInt();
		if(A<=9 && B<=9)
		{
			System.out.println(A*B);
		}
		else {
			System.out.println("-1");
		}

	}

}