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

    max_delicious = [[0, 0] for _ in range(N+1)]

    max_delicious[1] = [V[0], 1]

    for idx, value in enumerate(V[1:], 2):
        if max_delicious[idx-1][1]:
            if max_delicious[idx-2][0] + value > max_delicious[idx-1][0]:
                max_delicious[idx] = [max_delicious[idx-2][0] + value, 1]
            else:
                max_delicious[idx] = [max_delicious[idx-1][0], 0]
        else:
            max_delicious[idx] = [max_delicious[idx-1][0] + value, 1]

    print(max_delicious[N][0])


if __name__ == "__main__":
    main()