#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a,b,ans;
	cin>>a>>b;
	if(a>9||b>9)
		ans=-1;
	else
		ans=a*b;
	cout<<ans;
} 
### 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<bits/stdc++.h>
using namespace std;
int main()
{
	int a,b,ans;
	cin>>a>>b;
	if(a>9||b>9)
		ans=-1;
	else
		ans=a*b;
	cout<<ans;
} 
```