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

INF = (-1) * 10 ** 10

dp_o = [ INF ] * N
dp_x = [ INF ] * N

dp_o[0] = V[0]
dp_x[0] = 0

for i in range(1, N):
    dp_o[i] = dp_x[i - 1] + V[i]
    dp_x[i] = max(dp_o[i - 1], dp_x[i - 1])

print(max(dp_o[N - 1], dp_x[N - 1]))