n = int(input())
v = list(map(int, input().split()))
ans = 0
for ptn in range(1<<n):
    cnt = 0
    k = -1
    for i in range(n):
        bit = ptn >> i & 1
        if bit == k:
            break
        if bit:
            cnt += v[i]
            k = 1
        else:
            k = -1
    else:
        ans = max(ans, cnt)
print(ans)