import java.io.*;
import java.util.*;
 class Main
{
public static void main(String arg[])
{
Scanner s=new Scanner(System.in);
int a=s.nextInt();
int b=s.nextInt();
if(a>=1 && a<=9 && b>=1 && b<=9)
System.out.println(a*b);
else
System.out.println("-1");}}