import java.util.Scanner;
 class Main{
public static void main(String[] args){
  
  Scanner stdIn = new Scanner(System.in);
  
  int a = stdIn.nextInt();
  int b = stdIn.nextInt();
  	if (( a < 10 && b < 10)&&(a>0 && b >0;){
      System.out.println(a*b);
    }else{
      System.out.println(-1);
      
    }
}
 }