import java.util.*;

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 && B >= 1 && B <= 9) {
			System.out.println(A * B);
		} else {
			System.out.println(-1);
		}
		
	}

}




