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 s = new Scanner(System.in);
        int X = s.nextInt(), Y = s.nextInt();
        
        if(X % Y == 0){
            System.out.println(-1);
            return;
        }
        int n = 1000000000 / X + 1;
        for(int i = 1; i<n; i++){
            if((X * i) % Y != 0){
                System.out.println(X * i);
                break;
            }
        }
        
    }
    
}