Meine Tochter - Deine Tochter(1972)

Dr. Oskar Sommer, a good-natured high school teacher, takes on a momentous task for the school janitor, also named Oskar Sommer: he is to play the role of the janitor's daughter's father for a few days. Since the real father has not been seen for 15 years and has pretended to be a teacher in his letters, the two Sommers promptly pick up the wrong person at the train station.