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.

2 5

10

$2 \times 5 = 10$.

5 10

-1

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

9 9

81