How many years of college does it take to be an RN (registered nurse)?

I'm wondering how many years of college (university, in my case) does it take to be an RN?

I'm getting my CNA before college (during high school, I'm a senior), so I'll have some background in nursing.

How many years of college? I know it takes about 2 years of generals, but that's all I know...
I'm getting my CNA first so I can work as that before college to save up some money & gain experience to make sure I want to even go into nursing for sure...

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