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

take = [0] * (N + 1)
stay = [0] * (N + 1)
for i, a in enumerate(A, 1):
    # とるとき
    take[i] = stay[i - 1] + a
    # とらない
    stay[i] = max(stay[i-1], take[i-1])


ans = max(take[N], stay[N])
print(ans)