in phoenix. It is known that between every pair of planets either a single fire burns or no burning occurs.
If we consider any subset of $2019$ planets, the total number of fires burning between these planets is a
constant. If there are $F$ fires in phoenix, then find all possible values of $F$.
I have not understood the problem. Please help me to understand it. [Note: I am not good at English.
![Sad :(](./images/smilies/icon_e_sad.gif)