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;

class Main
{
	public static void main(String a[])
	{
		Scanner sc=new Scanner(System.in);
		int x=sc.nextInt();
		int y=sc.nextInt();
		if(x%y==0 || x==y)
		{
			System.out.println("-1");
			System.exit(0);
		}
		else if(y%x==0)
		{
			if((2*x)%y==0 || (2*x)==y)
			{
				System.out.println(3*x);
			}
			else
			{
				System.out.println(2*x);
			}
		}
		else
		{
			for(int i=2;i<10;i++)
			{
				if((i*x)%y!=0)
				{
					System.out.println(i*x);
					System.exit(0);		
				}
			}
			
		}
	}
}