max_sum = 0
def rote(current, sum, vn):
    global max_sum
    if current == n-1 or current == n-2:
        if (sum > max_sum):
            max_sum = sum

    if (current + 2 < n):
        rote(current + 2, sum + vn[current + 2], vn)
    if (current + 3 < n):
        rote(current + 3, sum + vn[current + 3], vn)

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

rote(-2, 0, vn)
print(max_sum)