import java.util.Scanner;
public class Main {
  public static void main(String args[]){
    Scanner nine = new Scanner(System.in);
    int number1 = nine.nextInt();
    int number2 = nine.nextInt();

    if(1<=number1 && number1<=9 && 1<=number2 && number2<=9){
      int answer = number1*number2;
      System.out.println(answer);
    }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