Blocking stackexchange

I want to block every website on the stackexchange network (as I often tend to waste a lot of time on those). How can I do it?

One solution is to obviously write all the sites' entries manually in the hosts file, but is there a better solution?

Note that just blocking on the regex *.stackexchange.com won't work as a lot of websites have unique names like superuser and askubuntu.

I am using Ubuntu 16.04.

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