class Main {
  public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
    if((a > 0) && (a < 10) && (b > 0) && (b < 10)) {
      System.out.println(a * b);
    } else {
      System.out.println(-1);
    } 
  }
}