Problem Statement

In the Kingdom of Enjapma, there is a custom of giving a tuple of $3$ natural numbers to one's neighbors as a present.
A tuple of $3$ natural numbers is called a "beautiful tuple" when it satisfies the following $2$ conditions, where the tuple consists of those $3$ natural numbers.

Condition $1$. The $3$ numbers are pairwise distinct natural numbers (integers greater than or equal to $1$).
Condition $2$. The sum of any $2$ of the natural numbers is a multiple of the remaining $1$ number.

As a greeting upon entering the country, you have also decided to give a "beautiful tuple" to your neighbor.
You have $2$ natural numbers $A,B$. Output one value: the minimum $C$ such that the tuple $(A,B,C)$ is a "beautiful tuple".
If no such $C$ exists, output $-1$.
It can be proven that, under these constraints, if a solution exists, its value is at most $10^{18}$.

Input

$A$ $B$

$A$ and $B$ are integers
$1 \le A \le 10^9$
$1 \le B \le 10^9$
$A$ and $B$ are distinct

Output

Output the minimum $C$ such that the tuple $(A,B,C)$ is a "beautiful tuple".
If it does not exist, output $-1$.

Sample

3 1

2

4 1

-1