Straight: adverb or adjective?

[Chicken Sandwich]

I'm curious whether "straight" is more commonly used as an adverb or adjective in the following context:

I've been reading this book for two weeks straight.

or

I've been reading this book for two straight weeks.

Somehow using "straight" as an adverb makes more sense to me (maybe it's more common to use it this way), but I've consultedd my dictionary, and there it says that "straight" can also be used as an adjective in this context, which makes both sentences equally good.

Are both sentences fine? Or is the first better, as my intuition tells me?

Thanks.

 

[Tdol]

What is it modifying- the book or the reading?

 

[Chicken Sandwich]

The reading. The idea is that I've been reading this book over a period of two weeks, non-stop.