    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);
        }
      }
    }