def strategy_expensive(cookies, cps, history, time_left, build_info):
    """
    Always buy the most expensive item you can afford in the time left.
    """
    #Clone BuildInfo object
    upgrades = build_info.clone()
    #Initially store zero
    item_cost = 0.0
    expensive_item = ""
    #Compare costs of items and store expensive item name
    for item in upgrades.build_items():
        temp_cost = upgrades.get_cost(item)
        if temp_cost > item_cost and temp_cost <= (time_left * cps + cookies):
            expensive_item = item
            item_cost = temp_cost
    if expensive_item == "":
        return None
    else:
        return expensive_item