Once upon a time in a land far, far away there lived 100 knights, 99 princesses, and 101 dragons. Over time, knights beheaded dragons, dragons ate princesses, and princesses poisoned knights. But they always obeyed an ancient law that prohibits k*****g any creature who has killed an odd number of others.
Eventually only one creature remained alive. Could it have been a knight? A dragon? A princess?
I believe this site should help you a bit: https://sites.math.washington.edu/~mathcircle/mathhour/olympiad_2015/15set57.pdf, but I'm not sure. I belive it should be a knight.