import java.util.Scanner;
        public class Main{
          public static void main(String[] args){
            Scanner stdIn = new Scanner(System.in);
            int a = stdIn.nextInt;
            int b = stdIn.nextInt;
            int c = a*b;
            if((a<1)||(a>9)||(b<1)||(b>9)){
              System.out.println("-1");
            }else{
              System.out.println(c);
            }
          }
        }