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.*;

public class Main{
    public static void main(String[] args) {
	Scanner sc = new Scanner(System.in);
	Long X = sc.nextLong();
	Long Y = sc.nextLong();
	if ( X % Y == 0 ) System.out.println(-1);
	else {
	    for ( int i = 2; X * i <= 1e18; i++ ) {
		if ( X * i % Y != 0 ) {
		    System.out.println(X * i);
		    return;
		}
	    }
	    System.out.println(-1);
	}
    }
}