I've included three versions here. The first is what I'd consider intermediate and is the one I'd focus on.
This second version is based on the accordion playing of Viljo Vesterinen. It is the main version that most people seem to play, although it does not include the key change to Fm for the last section. It is pretty close to the first version, but the melody in the last part has a bit more complexity.
This third version has been moved to Dm and has been simplified a bit. The melody basically follows the tune when it is sung. The last section here is a transitional part in case you'd like to either leave it out or use it as a segue into what's normally the last section. If you want to include the key change for typical last section, then transpose to Gm instead of Dm.
