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Score : $100$ points

### Problem Statement

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.

### Sample Input 1

2 5


### Sample Output 1

10


$2 \times 5 = 10$.

### Sample Input 2

5 10


### Sample Output 2

-1


$5\times 10 = 50$, but Takahashi cannot do this calculation, so print -1 instead.

### Sample Input 3

9 9


### Sample Output 3

81