instruction: Given a reference text about S26, tell me where it begins and ends.
context: S26 is a line on the Berlin S-Bahn. It runs from Teltow in the district (Kreis) of Potsdam-Mittelmark via Südkreuz, through the Berlin Nord-Süd Tunnel with a stop at Friedrichstraße, and ends in Waidmannslust in the borough of Reinickendorf. On weekends the S26 runs from Teltow to Potsdamer Platz.
  
  Trains on this line run every 20 minutes. This interval is in sections shortened to a 10-minute interval by the S25. There is no night service on this line.
response: S26 begins in Tetlow and ends in Waidmannslust.