import java.util.*;
import java.io.*;
import java.lang.*;
// ArrayList<Integer>[] arr=new ArrayList[n];
public class Main{    
public static void main(String[] args) throws FileNotFoundException, IOException{
        Scanner s = new Scanner(System.in);
         StringBuilder sb=new StringBuilder();
         BufferedWriter out=new BufferedWriter(new OutputStreamWriter(System.out));
         int n=s.nextInt(),m=s.nextInt();
         if(n<=9&&m<=9){
            System.out.println(n*m);
         }
         else{System.out.println("-1");}
       // System.out.println(sb);
    }
}
/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