import java.util.*;
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);
		}
	}
}