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<10 && B<10){
      System.out.println(A*B);
        }else{
      System.out.println("-1");          
}
}
}
