Help ID My Cactus! =)

Hi! So I just bought this super cute cactus at the store; but they have no information on what they are called. So I was just curious if anybody could help. Its green on the bottom, with no spikes. Kinda waxy; and then it's pink on top with spikes.. I need to know how often to water it so I need to know what kind it is. If you can help, I'd appreciate it. =)

 

This is my cactus:

 

And his name is Steve. xDD
I wonder when I should water him. =S But like I said, I need to find out what kind he is first..

 

Gymnocalycium mihanovichii I believe.

HTH
Chris

 

That would be it!! Thanks so much!