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();
		int answer = -1;

		if (1 <= A && A <= 9 && 1 <= B && B <= 9) answer = A * B;

		System.out.println(answer);
	}
}
