n = int(input())
v = list(map(int, input().split()))

dp = [0] * (n + 2)
dp[0], dp[1], dp[2] = 1, v[0], v[1 % n]

for i in range(3, n + 1):
    dp[i] = max(dp[i - 2], dp[i - 3]) + v[i - 1]

print(max(dp[n], dp[n - 1]))