Question 69
In a certain country there are exactly $2019$ cities, and between any two of them there is exactly one direct flight operated by some airline; that is, given cities $A$ and $B$, either there is a flight from $A$ to $B$ or a flight from $B$ to $A$. Find the smallest number of airlines operating in the country, knowing that the direct flights among any three distinct cities are operated by different airlines.