states_needed = set(["mt", "wa", "or", "id", "nv", "ut", "ca", "az"])

stations = {}
stations["kone"] = set(["id", "nv", "ut"])
stations["ktwo"] = set(["wa", "id", "mt"])
stations["kthree"] = set(["or", "nv", "ca"])
stations["kfour"] = set(["nv", "ut"])
stations["kfive"] = set(["ca", "az"])

final_stations = set()

while states_needed:
    best_station=None
    states_covered=set()
    for station,states_for_station in stations.items():
        covered=states_needed&states_for_station
        if len(covered)>len(states_covered):
            best_station=station
            states_covered=covered
    states_needed-=states_covered
    final_stations.add(best_station)

print(final_stations)