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);
    }
  }
}