Trains are sorted into categories which dictate the number of stops on a route, their priority on the network, and their fare structure. Each express train is identified by a five-digit number. If the first digit in the train number is 1 or 2, they are long-distance express trains. If the first digit is 0, the train is a special train which will operate for a limited period of time with a different fare structure. A first digit of 5 denotes a passenger train.