So, mum and dad bought a cactus

Woke up to noticed mum and dad assembling soil and cactus in a pot. Curious as to why they bought cactus. It was because I wanted one on my desk but I don't want it in the end. And now they bought one but it was too big to be place in my room so it was put on the corridor. No idea what's it is called, even after looking through the web. Shall try to document its growth every first day of the month :D