A 5th grade math textbook. According to the terms of the problem, every day a Pedestrian goes from point "A" to point "B", and along the way he meets a Cyclist. Then he returns home, where his faithful wife is waiting for him. The next day, everything repeats itself. But one day, the Pedestrian is stopped by the Investigator, who tells him that the Cyclist has disappeared. The Investigator asks the Pedestrian to go with him to point "B" to question witnesses and sort out this confusing story together.