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

a = V[:2] + [0] * (N-2)

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

print(max(a[N-2:]))