import java.util.Scanner;
import java.util.*;
public class Main {
	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int a = scn.nextInt();
		int b = scn.nextInt();
		if(a>=1 && a<=9) {
			if(b>=1 && b<=9) {
				System.out.println(a*b);
			}
			else {
				System.out.println(-1);
			}
		}
		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