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

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

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])