Any suggestions please?
I'm a complete newbie at graph theory, so I guess this is something really stupid.

Solved it.
It wasn't actually a WA but a RT. The point is, #17 seems to contain 300 names with no Isenbaev. Thus, if you always give some fixed ID (say, zero) while giving other people other IDs, you will have an "index out of bounds" exception. My program caught that exception, printed stack trace (as you might have already guessed, my program is in Java) and exited with exit code 9000. Since stack trace is printed in stdout, Timus's checking system couldn't parse that output which resulted in WA.

*if you always give HIM some fixed ID, of course

Thank you very much.I got AC.>-<

because, array need more than 300!!