N = int(input())
V = list(map(int, input().split()))

from itertools import combinations

n = [_ for _ in range(N)]
ans = 0
for i in range(1, N+1):
    for j in combinations(n, i):
        # print(j)
        v = 0
        judge = True
        for k in range(i-1):
            if j[k]+1 == j[k+1]:
                judge = False
                break
            else:
                v += V[j[k]]
        if judge:
            v += V[j[-1]]
            # print(j,v)
            ans = max(ans, v)

print(ans)