I am pretty sure that during Educational Codeforces Round 100 (Rated for Div. 2), buihoatpt2k3 copied code from huyhoangk36chv.
buihoatpt2k3's behavior is quite suspicious in general — he (?) submitted all his code during the last 30 minutes, and his code is heavily obfuscated.
We see, however, that after running the preprocessor (gcc -E) on the code, we get code that is strikingly similar to that of huyhoangk36chv.
I think this is pretty good evidence that these users cheated and copied code from each other, and as such, call for their participation in the contest to be voided.