import java.util.Scanner;

public class Main {
	
		public static void main(String[] args) {
			
			Scanner sc =new Scanner(System.in);
			
			
			int a,b;
			a=sc.nextInt();
			b=sc.nextInt();
			
			if(a>9||b>9) {
				System.out.println(-1);
				
			}
			else {
				System.out.println(a*b);
			}
			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