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

ans = 0
while len(V) > V.count(0):
    if len(V) < 3:
        ans += max(V)
        break
    a = []
    for i in range(len(V)-2):
        a.append(V[i] + V[i+2])
    t = a.index(max(a))
    c0 = V[t]
    c1 = V[t+2]
    if c0 > c1:
        ans += c0
        if t > 0:
            V[t-1] = 0
        V[t] = 0
        V[t+1] = 0
    else:
        ans += c1
        if t+3 < len(V):
            V[t+3] = 0
        V[t+2] = 0
        V[t+1] = 0
print(ans)