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);
		int X = sc.nextInt();
		int Y = sc.nextInt();

		int xa = X*2;
		if(X%Y == 0) {
			System.out.println(-1);
			return;
		}

		while(xa%Y == 0 && xa < Math.pow(10, 18)) {
			xa += X;
		}

		if(xa > Math.pow(10, 18)) {
			System.out.println(-1);
		}else {
			System.out.println(xa);
		}
	}
}