import java.util.Scanner;
 class Main{
public static void main(String[] args){
  
  Scanner stdIn = new Scanner(System.in);
  
  int a = stdIn.nextInt();
  int b = stdIn.nextInt();
  	if ( a < 10 && b < 10){
      System.out.println(a*b);
    }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