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<=9 && B<=9){
  int c=A*B;
  System.out.println(c);
}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