import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		Integer A = sc.nextInt();
		Integer B = sc.nextInt();

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

}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz