java.util.Scanner;
public class Main{
  public static void main(String[] args){
    Scanner stdIn = new Scanner;
    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);
    }
  }
}