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

p = [0] * N
if N >= 3:
    p[0] = v[0]
    p[1] = v[1]
    p[2] = p[0] + v[2]
    for i in range(3, N):
        p[i] = max(p[i-2] + v[i], p[i-3] + v[i])
    result = max(p[N-2], p[N-1])
elif N == 2:
    result = max(v[0], v[1])
elif N == 1:
    result = v[0]
print(result)