import java.util.*;

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");
    }
  }
}