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>=1 && a<=9 && b>=1 && b<=9){
      System.out.println(a*b);
    }else{
      System.out.println(-1);
    }
  }
}
