Who is singing there?

The story of this film took place in 1941, during the German army's sweep across Europe. It begins with the singing of two poor teenagers who are about to go to Belgrade, and the story unfolds from the bus they take. All kinds of people got on this car, retired soldiers, two rich people, newlyweds, the driver and his son. Various accidents lead to various stories, narratives and activities: being stopped by soldiers at an intersection; having a tire punctured by a farmer on another road who was charging money to buy the road; while resting by the lake, he met a marching foreign team, the car was requisitioned, and when he came back, the driver's son had been forced to join the army; the retired soldier's wallet was dropped on the road, but the passengers suspected two poor teenagers and beat them up. In the end, the car was burned and toppled under the bombing of German planes, but the two teenagers with dirty faces still climbed out of the car window and continued singing... The trip to Belgrade ended with difficulty.