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 sc = new Scanner(System.in);
		long x = sc.nextInt();
		long y = sc.nextInt();
		long a = 1000000000;
		a = a * a;
		long z;
		boolean e = false;
		if (x != y && x % y != 0) {
			int i = (int)(y / x);
			for (; x*i <= a; i++) {
				z = x * i;
				if ((z % y) != 0) {
					System.out.println(z);
					e = true;
					break;
				}
			}
		}
		if (!e)
			System.out.println("-1");
	}
}