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

dp = [0] * (N+1)

for i in range(1, N+1):
    a = (dp[i-2] if i-2 >= 0 else 0) + V[i-1]
    b = (dp[i-3] if i-3 >= 0 else 0) + V[i-1]
    dp[i] = max(dp[i], a, b)

print(dp[-1])