Automaticly change number

Hi everyone,
I hope I'm not repeating this issue I'm having. I would be very grateful if someone has a easy way to help me. I'm trying to make a scoring tool for a questionaire. Is there an easy and elegant formula to automaticly change the inserted numbers - all in one cell?

1 has to change to 3
2 has to change to 1
3 has to change to 0

Also:
0 => 0
1 => 0
2 => 1
3 => 2

Thank you so much for your help!

Relinqu