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

max_d = [0] * N
max_d[:2] = V[:2]

for i in range(2, N):
    # 2個前までのおいしさを加味
    max_d[i] = max_d[i-2] + V[i]
    # 3個前までのおいしさの方が凌駕してたらそっち採用
    if (i >= 3) and (max_d[i] < max_d[i-3] + V[i]):
        max_d[i] = max_d[i-3] + V[i]

print(max(max_d))