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

dp = [0] * N
dp[0] = V[0]
dp[1] = V[1]
for i in range(N - 2):
    if i + 2 < N:
        dp[i + 2] = max((dp[i + 2], dp[i] + V[i + 2]))
    if i + 3 < N:
        dp[i + 3] = max((dp[i + 3], dp[i] + V[i + 3]))

print(max(dp[-2:]))