Problem:
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.

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;


public class Main {

    public static void main(String[] args) {

    	Main main=new Main();

    	main.run();

    }

    void run() {

    	Scanner sc=new Scanner(System.in);


    	int A=sc.nextInt();
    	int B=sc.nextInt();

    	if(A%B==0) {
    		System.out.println("-1");
    	}else {
    		System.out.println(A);
    	}

    }
}