import itertools

N = int(input())
l = input().split(' ')
li = list(map(int, l))
lindexes = []
for i in range(len(li)):
    lindexes.append(i)
NM = int(N / 2) + 1
OISHISA = 0
for NMR in range(1, NM + 1):
    for lst in list(itertools.combinations(lindexes, NMR)):
        sum = 0
        present = -2
        for elm in lst:
            if max([elm - present, 0]) == 1:
                break
            sum += li[elm]
            present = elm
        if OISHISA < sum:
            OISHISA = sum
print(OISHISA)