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.*;
//import java.util.stream.Collectors;

public class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		int x = sc.nextInt();
		int y = sc.nextInt();
		int result = -1;
		if(x % y != 0){
			for(int i=x; ; i+=8){
				if(i % y != 0){
					result = i;
					break;
				}
			}
		}
		
		System.out.println(result);
	}
}