from functools import lru_cache
import sys

sys.setrecursionlimit(2000)

@lru_cache(maxsize=5000)
def osusi(N, V):
    if N == 1:
        return V[0]
    pat = [0, 0, 0, 0, V[-2], V[-1]]
    if N - 2 >= 1:
        pat[0] = osusi(N - 2, V[:N - 2]) + V[-1]
    if N - 3 >= 1:
        pat[1] = osusi(N - 3, V[:N - 3]) + V[-1]
        pat[2] = osusi(N - 3, V[:N - 3]) + V[-2]
    if N - 4 >= 1:
        pat[3] = osusi(N - 4, V[:N - 4]) + V[-2]
    return max(pat)

if __name__ == '__main__':
    N = int(input())
    V_li = tuple(map(int, input().split()))
    print(osusi(N, V_li))