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 >= 1 && a <= 9 && b >= 1 && b <= 9) System.out.println(a * b);
        else System.out.println(-1);

    }

}
