50. In the city, 2019 metro stations have been built. Some pairs of stations are connected by tunnels, and from any station, you can reach any other station via the tunnels. The mayor ordered the organization of several metro lines: each line must include several different stations, sequentially connected by tunnels (the same tunnel can be part of several lines). Each station must lie on at least one line. To save funds, no more than $k$ lines should be created.

It turned out that the mayor's order was impossible to implement. For what largest $k$ could this have happened? (S. Berlov)