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())
if x%y==0:
        print '-1'
else:
        i=2
        while x*i<10**18+1:
                if x*i%y!=0:
                        print x*i
                        break
                i=i+1

##t=[1]
##while t[len(t)-1]*2<=n:
##	t.append(t[-1]*2)
##x=0
##i=0
##while i<len(t) and x+t[i]<=n:
##	x=x+t[i]
##	i=i+1
##
##if n&(n+1)==0:
##	print n
##elif k==1:
##	print n
##else:
##	print 2*t[-1]-1