CTF all the day

hi guys, i have a problem, when i try to connect to ctf13.root-me.org in linux, a few moments charging the page gave me this message

The server at ctf13.root-me.org is taking too long to respond.

The site could be temporarily unavailable or too busy. Try again in a few moments.
If you are unable to load any pages, check your computer’s network connection.
If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the web.

anyone knows the solution ?