Having learned the multiplication table, Takahashi can multiply two integers between 1 and 9 (inclusive) together. He cannot do any other calculation.

Given are two integers A and B.

If Takahashi can calculate A \times B, print the result; if he cannot, print `-1` instead.

Constraints

* 1 \leq A \leq 20
* 1 \leq B \leq 20
* All values in input are integers.

Input

Input is given from Standard Input in the following format:


A B


Output

If Takahashi can calculate A \times B, print the result; if he cannot, print `-1`.

Examples

Input

2 5


Output

10


Input

5 10


Output

-1


Input

9 9


Output

81
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int a=scan.nextInt();
		int b=scan.nextInt();
		if(a>0 && a<=9 && b>0 && b<=9) System.out.println(a*b);
		else System.out.println("-1");
	}

}
