def filter_onlyCheapest(itineraries, count=1):
    """
    filter the input itineraries and select the cheapest one

    :param itineraries: input itineraries
    :param count: number of itineraries needed to get after filtering
    :return: cheapest itineraries
    :rtype: list
    """
    itineraries.sort(key=lambda x: x.getCheapestPriceOptions()[0])
    return itineraries[:count]