sorry for bad england I woke

Seen noftication

-is-this-fft- mention me

he call me stupi

how dare u?

dare u my frend

Screenshot from ~9 years ago Codeforces Beta! http://funkyimg.com/i/2M6zq.png

Copyrights to my friend

I recently spotted this problem of IOI 2018. I couldn't come up with a proper approach. Only thing that I know is the solution is associated with graph. Can you please help me to solve this problem?

https://ioi2018.jp/wp-content/tasks/contest1/werewolf.pdf