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:
X, Y = map(int, raw_input().split())

#print X, Y

count=2

num = X
flag = False

if X % Y == 0:
    print -1
else:
    while num <= 1000000000000000000 :
        num = X * count
        if (num % Y) != 0:
            #        print num
            flag = True
            break
        else:
            count = count +1

    if flag == False:
        print -1
    else:
        print num