Problem 4. Seven cities are connected in a circle by seven one-way flights (see figure). Assign (draw with arrows) several more one-way flights so that from any city to any other, one could get there with no more than two transfers. Try to make the number of additional flights as small as possible.

![](https://cdn.mathpix.com/cropped/2024_05_06_5f8bb630dfa91fa0065fg-2.jpg?height=273&width=277&top_left_y=1428&top_left_x=998)

(up to 6 points) (V.A. Klepinin)
Solution. An example with five additional flights is shown in the figure. It can be proven that it is impossible to add a smaller number of flights.

![](https://cdn.mathpix.com/cropped/2024_05_06_5f8bb630dfa91fa0065fg-3.jpg?height=294&width=297&top_left_y=279&top_left_x=578)