"""回転寿司"""

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

if N == 1:
    print(V[0])
else:
    v = [0] * (N+10)
    max_go_back_two = V[0]
    v[0] = V[0]
    v[1] = V[1]
    for i in range(2, N):
        v[i] = max(max_go_back_two + V[i], V[i])
        max_go_back_two = max(max_go_back_two, v[i-1])
    print(max(v))