I'm not an expert by any means, but I'd say four:  un +imagin(e) + ative + ly

I'd say the root morpheme is the verb 'imagine'.  Some people might try to split it down further (" image + ine  = imagine", like " exam + ine = examine"), but I'm not sure that works.

The three bound morphemes which are attached to it are:

'un' to make it negative.

'ative' to make the verb into an adjective

'ly' to make the adjective into an adverb

Thanks a lot for all the effort [emoji][emoji]♥️ that was really helpful !