being integrated into the Brussels Regional Express Network (French: Réseau Express Régional Bruxellois, RER; Dutch: Gewestelijk ExpresNet, GEN), which is identified by the letter S across both languages. In 2018, the S-train was also introduced in Antwerp, Ghent, Liège and Charleroi. Czech Republic In the Czech Republic, integrated commuter rail systems exist in Prague and Moravian-Silesian Region. Both systems are called Esko, which is how S letter is usually called in Czech. Esko Prague has been operating since 9 December 2007 as a part of the Prague Integrated Transport system. Esko Moravian-Silesian Region began operating on 14 December 2008 as a part of the ODIS Integrated Transport system serving the Moravian-Silesian Region. Both systems are primarily operated by České dráhy. Several shorter lines are operated by other companies. Denmark Copenhagen S-train connects the city centre, other inner and outer boroughs and suburbs with each other. The average distance between stations is 2.0 km, shorter in the city core and inner boroughs, longer at the end of lines that serve suburbs. Of the 86 stations, 32 are located within the central parts of the city. Some stations are located around 40 km from Copenhagen city centre. For this reason the fares vary depending on distances. The one-day passes which the tourists buy are valid only in the most central parts of the S-train system. On weekdays each line has a departure every 10 minutes with the exception of the F-line, on which a train departs every five minutes. Where several lines converge on a common piece of track there could be as many as 30 trains per hour in each direction. On Sundays the seven lines are reduced to four lines, but all stations are served at least every 10 minutes. The three railway stations at Amager have a local service that is the equivalent of the S-trains. The Copenhagen Metro opened in 2002 as a complement to the already existing S-train system. Copenhagen's S-train system is the only one in the country. Outside Denmark, in cities where both exist, is it far from unusual that a metro system later has been complemented with S-trains. The branch towards Køge (the southernmost S-train station in Copenhagen's S-network) has a rather unique history, as it was built in the 1970s where no previous railway ever had existed. Germany The trains of the Berlin and Hamburg S-Bahn systems ran on separate tracks from the