def memorize(f):
    cache = {}
    def helper(x, y):
        if (x, y) not in cache:
            cache[(x, y)] = f(x, y)
        return cache[(x, y)]
    return helper

@memorize
def kaitenzusi(susi_number,before_get):
    if susi_number == N:
        return 0
    not_get = 0 
    if before_get == False:
        not_get = kaitenzusi(susi_number+1, True) + V[susi_number]
    get = kaitenzusi(susi_number+1, False) 
    return not_get if not_get > get else get

N = int(input())
V = [int(num) for num in input().split()]
print(kaitenzusi(0, False))