"""

Mは高々30ぐらい

"""

import sys
from sys import stdin

def popcnt(a):
    ret = 0
    while a > 0:
        ret += a % 2
        a //= 2
    return ret

X = int(stdin.readline())

for i in range(40):

    N = X ^ i
    if popcnt(N) == i:
        print (N)
        sys.exit()

print (-1)