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[] args){
		
		Scanner s = new Scanner(System.in);
		long x=s.nextLong();
		long y=s.nextLong();
		
		Long z=(long)Math.pow(10, 18);
		
		while(x<z){
			long t= x/y;
			if(t*y==x){
				x+=x;
			}
			else{
				System.out.println(x);
				System.exit(0);
			}
		}
		System.out.println(-1);
		
	}
}