from itertools import takewhile, accumulate, repeat, chain
from operator import floordiv

normal = [i for i in takewhile(lambda x: x > 0, accumulate(chain([int(input())], repeat(2)), floordiv))]
special_max = max([sum(normal[:i], normal[i] * 2) for i in range(len(normal))])
print(special_max - sum(normal))