import java.util.*;
import java.lang.*;




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<10 && B<10) System.out.println(A*B);
        else System.out.println(-1);


    }
}
