from itertools import accumulate

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

ae = list(accumulate([0] + A[0::2]))
ao = list(accumulate([0] + A[1::2]))

ans = -10**17
for i in range(N+1):
    homu = ae[i] - ae[0] + ao[N] - ao[i]
    ten = ao[i] - ao[0] + ae[N] - ae[i]
    s = homu - ten
    if s > ans: ans = s
print(ans)