import java.util.*;
import java.io.*;
public class Main {

    public static void main (String[] args) throws java.lang.Exception
{
    BufferedReader inp = new BufferedReader (new InputStreamReader(System.in));
    String[] s1 = inp.readLine().split(" ");
    int A = Integer.parseInt(s1[0]);
    int B = Integer.parseInt(s1[1]);
    if(A<=9 && A>=0 && B<=9 && B>=0){
        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