import java.util.*;

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");
    }
  }
}