import java.util.Scanner;
 
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 && b <= 9){
        System.out.println(a*b);
      }else{
        SYstem.out.println(-1);
      }
      
      sc.close();
    }
}
