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||y==1){
      	System.out.println(-1);
        return;
      }
     for(long i = x;i <= (long)Math.pow(10,18);i+=x){
     	if(i%y!=0){
        	System.out.println(i);
          return;
        }
     }
      System.out.println(-1);
    }
}