OPM 2019 Problem 6

A metro network with $n \ge 2$ stations, where each station is connected to each of the others by a one-way line, is said to be dispersedi f there are two stations $A$ and $B$ such that it is not possible to go from $A$ to $B$ through is from the network. If a network is dispersed, but it is possible to choose a station $A$ and reverse the direction of all lines to and from $A$ so that the new network is no longer dispersed, the network is said to be correctable. Indicates all integers $n$ for which there is a network with $n$ stations, dispersedand not correctable.