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:
a, b = map(int, raw_input().split())

if a == b:
    print(-1)
elif a > b and a%b == 0:
    print(-1)
else:
    x = a
    mult = 2
    fuck = False
    while (x * mult) % b == 0:
        mult = mult + 1
        if x * mult > 1e18:
            break
    if (x * mult)%b != 0 and x * mult <= 1e18:
        print(x*mult)
    else:
        print(-1)