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) {
		Main m = new Main();
		m.run();
	}

	Scanner sc = new Scanner(System.in);

	void run() {

		int n = sc.nextInt();
		int m = sc.nextInt();

		if(n%m == 0){
			System.out.println(-1);
			return;
		}
		
		long max = 1000000000000000000L;
		
		for(long x = n;x <= max; x+=n){
			if(x % m != 0){
				System.out.println(x);
				return;
			}
		}
		System.out.println(-1);
		
	}
}