RoAlgo Weekly Contest #1 | inmultire

Task

After he memorized the multiplication table, Gigel can now multiply two integers between $1$ and $9$ (including $1$ and $9$), without being able to perform other multiplications.

Given two integers $a$ and $b$, figure out whether Gigel can multiply them or not. If he can do it, print ($a \cdot b$), otherwise print $-1$.

Input data

The first line of the input contains two integers, $a$ and $b$.

Output data

The output will contain a single integer, ($a \cdot b$) if Gigel can multiply them, otherwise print $-1$.

Constraints and clarifications

• $1 \leq a, b \leq 20$

Example 1

stdin

7 6

stdout

42

Example 2

stdin

5 12

stdout

-1