import java.util.Scanner;
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<10 && a>0 && b<10 && b>0){
			System.out.println(a*b);
		}else{
			System.out.println(-1);
		}
	}
}
