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

• $1 ≤ X,Y ≤ 10^9$
• $X$ 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.

Sample Input 1

8 6

Sample Output 1

16

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

Sample Input 2

3 3

Sample Output 2

-1

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