import java.util.*;

public class Main{
	public static void main(String[] args){
      Scanner input = new Scanner(System.in);
      int a = input.nextInt();
      int b = input.nextInt();
       if((a <1 && a>9) || (b <1 && b>9)){
         	System.out.println(-1);
       } 
      	else{
          System.out.println(a*b);
        }  
    }
} 