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.*;

class Main {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);

        long x = sc.nextLong();
        long y = sc.nextLong();

        long a = x * y;

        for (long i = x; i <= a; i += x) {
            if (x % y != 0) {
                System.out.println(x);
                return;
            }
        }

        System.out.println(-1);
    }
}