n = int(input())
v = list(map(int, input().split()))

routes = [[1]]
flag = True

ans = []

while flag:

    flag = False
    r = []

    for route in routes:

        if route == []:
            continue

        if route[-1] < n:
            r.append(route + [route[-1] + 2])
            r.append(route[:-1] + [route[-1] + 1])
            flag = True
        elif route[-1] == n:
            ans.append(route)
            ans.append(route[:-1])
        else:
            ans.append(route[:-1])

    if flag == True:
        routes = r

else:

    score = []

    for a in ans:
        s = 0
        for i in a:
            s += v[i-1]
        score.append(s)

    print(max(score))