import java.io.PrintWriter;
import java.util.Scanner;
 
public class Main {
 
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);
		int A = Integer.parseInt(sc.next());
        int B = Integer.parseInt(sc.next());
        if(1<=A&&A<=9&&1<=B&&B<=9){
          out.println(A*B);
        }
        else{
          out.println(-1);
        }
		
 
		out.flush();
	}
}
/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