import java.util.Scanner;

public class Main{
  public static void main(String args[]){
    Scanner scan=new Scanner(System.in);
    int A=scan.nextInt();
    int B=scan.nextInt();
    if (((1<=A) && (A<=9))&&((1<=B) && (B<=9))){
      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