def main():
    n = int(input())
    m = list(map(int, input().split()))

    dp_list = [0] * n
    dp_list[0] = m[0]
    if 1 < n:
        dp_list[1] = max(m[0], m[1])
        for index in range(2, n):
            dp_list[index] = max(dp_list[index - 2] + m[index], dp_list[index - 1])
        print(max(dp_list))
    else:
        print(m[0])


if __name__ == '__main__':
    main()