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

if N == 1:
    print(sushi_plates.pop())
    exit()

else:
    answers = [0] * (N + 1)
    answers[1] = sushi_plates[0]
    for i in range(2, N + 1):
        answers[i] = max(answers[i - 1], answers[i - 2] + sushi_plates[i - 1])

print(answers[N])