import java.util.*;
import java.lang.*;
import java.io.*;

public class Main {
 	public static void main (String[] args) {
      Scanner sc = new Scanner (System.in);
      int a = sc.nextInt();
      int b = sc.nextInt();
      
      System.out.println(a<10&&b<10 ? a*b : "-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