import java.util.Scanner;
 
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){
    		if(b < 10){
        		System.out.println(a * b);
            
        	}else{
        		System.out.println(-1);
        	
            }
    	}else{
            	System.out.println(-1);
        }
    }
}
/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