Early adopter for a lot of things, so yeah 4 which is easily verifiable.
I've been using Ubuntu since at least 2005DEC31 ~ http://www.flickr.com/photos/bootload/79685287/ and "... the first release was Ubuntu 4.10 as it was released on 20 October 2004 ..." ~ http://en.wikipedia.org/wiki/Ubuntu_%28operating_system%29#R...