
import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		//intを受け取る
		int a = sc.nextInt();
		int b = sc.nextInt();
		
		if(a<=9 && b<=9) {
			System.out.println(a*b);
		}else {
			System.out.println("-1");
		}
	}
}
