#include <bits/stdc++.h>

using namespace std;

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

In Cpp, your task is to solve the following problem:

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 <bits/stdc++.h>

using namespace std;

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