[*] Switching to interactive mode
# $ id
uid=1000(observer) gid=1000(observer) euid=0(root) groups=1000(observer)
# $ cd /root
# $ ls -l
total 12
-rwx------ 1 root root 819 Nov 10 14:27 broadcast.py
-rwx------ 1 root root 905 Sep 13 18:39 connection.py
-r-------- 1 root root 33 Sep 5 03:41 root.txt
# $ cat root.txt
i got the root. 
it was very hard for me.but i learned a lot from this machine.
i have solved heap challenges before, but this one was new and hard.
thank you @MrR3boot @b14ckh34rt and @job0 @blink3r @v01t4ic for their helps