Problem: 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.

Examples

Input

8 6


Output

16


Input

3 3


Output

-1

Solution (in JAVA):

Solution:
import java.util.Scanner;
public class Main

{
    public static void main(String arg[])
    {
        int a,b;
        @SuppressWarnings("resource")
		Scanner scan=new Scanner(System.in);
        a=scan.nextInt();
        b=scan.nextInt();
        if(a%b==0||a==b)
        {
        	System.out.println(-1);
        	System.exit(0);
        }
        int c=a;
        while(2>1)
        {
            c=c+a;
            if(c%a==0&&c%b!=0)
            {
            System.out.println(c);
            break;
            }
            if(c>b&&a%b==0)
            {
                System.out.println("Hello"+-1);
            break;
            }
        }
    }
}