import java.util.Scanner;

class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int a= scan.nextInt();
		int b= scan.nextInt();
		scan.close();

		if( (1<a && a<10) && (1<b && b<10) )
		System.out.println(a*b);
		else
		System.out.println(-1);
	}
}