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 < 1 || a > 9) {
	    		System.out.println(-1);
	    	}
	    	if (b < 1 || b > 9) {
	    		System.out.println(-1);
	    	}
	    	System.out.println(a * b);
	}
}
