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