#include <iostream>
using namespace std;

int a, b;
int main() {
	cin >> a >> b;
	cout << (a<10 && b<10 ? a*b : -1);
	return 0;
}

### Prompt

Develop a solution in Cpp to the problem described below:

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

### Response

```cpp
#include <iostream>
using namespace std;

int a, b;
int main() {
	cin >> a >> b;
	cout << (a<10 && b<10 ? a*b : -1);
	return 0;
}

```