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>9 || b>9){
         	System.out.println(-1);
       } 
      	else{
          System.out.println(a*b);
        }  
    }
} 
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz