Score : $100$ points

Problem Statement

You are given positive integers $X$ and $Y$. If there exists a positive integer not greater than $10^{18}$ that is a multiple of $X$ but not a multiple of $Y$, choose one such integer and print it. If it does not exist, print $-1$.

Constraints

• $1 \leq X,Y \leq 10^9$
• $X$ and $Y$ are integers.

Input

Input is given from Standard Input in the following format:

$X$ $Y$

Output

Print a positive integer not greater than $10^{18}$ that is a multiple of $X$ but not a multiple of $Y$, or print $-1$ if it does not exist.

8 6

16

For example, $16$ is a multiple of $8$ but not a multiple of $6$.

3 3

-1

A multiple of $3$ is a multiple of $3$.