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 PYTHON):

Solution:
#!/usr/bin/env python
#-*- coding: utf-8 -*-

from collections import defaultdict
from math import factorial as f
from fractions import gcd as g

a, b = [int (i) for i in raw_input ().split ()]
l = a * b / g (a, b)
if l == a: print "-1"
elif l == 2 * a: print 3 * a
else: print 2 * a