import java.util.*;
public class Main {

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

	}

}
