from itertools import combinations


def is_continuous(iter):
    previous = None
    for v in iter:
        if previous is None:
            previous = v
            continue
        if v - previous == 1:
            return True
    return False


times = int(input())
data = [
    int(x)
    for x in input().split(' ')
]

max_length = int(times / 2 + times % 2)


result = -1
for i in range(max_length):
    length = i + 1
    for comb in combinations(range(times), max_length):
        tmp = 0
        if is_continuous(comb):
            continue
        for index in comb:
            tmp += data[index]
        if result < tmp:
            result = tmp
print(result)