def calc(N, ls):
    m1, m2 = 0, 0
    for i in range(N):
        m1, m2 = m2, max(m2, m1+ls[i])
    return m2

def main():
    N = int(input())
    ls = list(map(int, input().split()))
    res = calc(N, ls)
    print(res)

main()