import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new java.util.Scanner(System.in)
        int a = sc.nextInt(); int b = sc.nextInt();
        if (!(a >= 1 && a <= 9 && b >= 1 && b <= 9)) {
            System.out.println("-1");
        } else {
            System.out.println(a * b);
        }
    }

}