import java.util.*;

class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		int A = scanner.nextInt();
		int B = scanner.nextInt();

		if ((A > 9 || A < 1) || (B > 9 || B < 1)) {
			System.out.println("-1");
		} else {
			System.out.println(A * B);
		}
	}
}
/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