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 a = sc.nextInt();
        long b = sc.nextInt();
        sc.close();

        if (a == b) {
            System.out.println("-1");
            return;
        }

        if (a % b == 0) {
            System.out.println("-1");
        } else {
            System.out.println(a);
        }
    }
}