import java.util.*;
import java.math.*;
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 && a>=1) && (b<=9 && b>=1)
             System.out.println(a*b);
             else
             System.out.println("-1");
        }
}
