# coding; utf-8
N = int(input())
V = [0] + list(map(int, input().split()))

if N == 1:
    print(V[1])
    quit()
elif N == 2:
    print(max(V))
    quit()

memo = [0] * (N + 1)
memo[N] = V[N]
memo[N - 1] = V[N - 1]

for i in range(N - 2, 0, -1):
    memo[i] = V[i] + max(memo[i + 2:])

print(max(memo))