Contest Duration: - (local time) (300 minutes) Back to Home
A - Two Integers /

Time Limit: 2 sec / Memory Limit: 256 MB

### 制約

• 1 ≤ X,Y ≤ 10^9
• X,Y は整数

### 入力

X Y


### 出力

X の倍数であって Y の倍数でない 10^{18} 以下の正整数を一つ出力せよ。 存在しない場合は -1 を出力せよ。

### 入力例 1

8 6


### 出力例 1

16


### 入力例 2

3 3


### 出力例 2

-1


3 の倍数は 3 の倍数です。

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 ≤ 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.