def find_path(stages):

    city_paths = {} #dictionary of strings to strings
    potential_start_cities = set()
    for start_city, end_city in stages:
        city_paths[start_city] = end_city
        potential_start_cities.add(start_city)

    for key, end_city in city_paths.iteritems():
        if end_city in potential_start_cities:
            potential_start_cities.remove(end_city)

    assert len(potential_start_cities) == 1

    current_city = potential_start_cities.pop()

    paths = [current_city]

    while len(city_paths) > 0:
        paths.append(city_paths[current_city])
        start_city_temp = current_city
        current_city = city_paths[current_city]
        city_paths.pop(start_city_temp)

    return paths



stages = [('Bergerac','Pau'), ('Nice','Montpelier'), ('Pau','Paris'), ('Marseille','Nice'), ('Montpelier','Bergerac'), ('Chicago', 'NYC')]

print find_path(stages)