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.*;
 public class Main {
 	public static void main(String[] args){
 		Scanner sc = new Scanner(System.in);
 		// 整数の入力
 		int a = sc.nextInt();
 		int b = sc.nextInt();
 		// 出力
        if(a > 9 || b > 9)
          	System.out.println("-1");
        else
	 		System.out.println(a * b);
 	}
 }
