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)) {
		   System.out.println(-1);
	   }else if(!(B < 10)) {
		   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