N = int(input())
V = [int(i) for i in input().split()]


def sushi(ith, isSucce):
    if ith == N:
        return sushi(ith, True)
    if isSucce:
        return sushi(ith + 1, False)
    else:
        return max(sushi(ith + 1, True) + V[ith], sushi(ith + 1, False))


print(sushi(0, False))