XYZ CODE: watch tower

Hi, Earthian, since you have been here for a while, let's assume you have learned something, so here is a job for you on the watch tower.

Watch closely for the night sky, if a new star suddenly appears from nowhere, you should let us know. Good luck.

Oh, by the way, you are still single, right? If you know how to do connected components for a graph, you can write a program to watch the sky, then ... go dating, maybe.

How many stars are in the sky?