Given a reference text about S26, tell me where it begins and ends.

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.[1]

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.

S26 begins in Tetlow and ends in Waidmannslust.