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:
# vim: set fileencoding=utf-8 :
x, y = map(int, raw_input().split())

if x % y == 0:
    print(-1)
    exit()

n = 1
top = pow(10, 18)

while True:
    t = n * x
    if t >= top:
        print(-1)
        break

    if t % y != 0:
        print(t)
        break

    n += 1