import java.util.*;
public class Main{
  public static void main(String[] args){
Scanner sc=new Scanner(System.in);
int A=sc.nextInt();
int B=sc.nextInt();
if( A<=9 && B<=9){
  int c=A*B;
  System.out.println(c);
}else{
System.out.println("-1");
 }
  }
}
