def fibonacci_generator():
    """
    Fibonacci generator function that starts with 1, 1, 2, 3, ...

    :returns: generator that yields fibonacci numbers
    """
    a = 0
    b = 1
    yield b
    while True:
        a, b = b, (a + b)
        yield b


def fibonacci_generator_smaller(n):
    """

    :param n: generator yields all fibonacci numbers smaller n
    :returns: generator that yields fibonacci numbers

    """
    g = fibonacci_generator()
    x = next(g)
    while x < n:
        yield x
        x = next(g)


def fibonacci_nth(n):
    """

    :param n: index of fibonacci that should be returned
    :returns: nth fibonacci number

    """
    if n < 1:
        return 0
    g = fibonacci_generator()
    i = 1
    x = next(g)
    while i < n:
        i += 1
        x = next(g)
    return x