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

def solve(d, i, w):
    if -1 < i - 2 < n:
        w += a[i - 2]

    if i >= n:
        return w

    return max(solve(i, i + 2, w), solve(i, i + 3, w))

print(solve(0, 0, 0))