import java.util.*;

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

	int b = scan.nextInt();

	if( a >= 1 && a <= 9 && b>= 1 && b <=9)
		System.out.println(a * b);
	else
		System.out.println("-1");


	}


}
/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