Hi Andreyjv,

Thank you for your question. In my opinion there are many possible answers to your question rather than a simple yes or no.
Let me start by saying that 640 is not a low score. Its certainly not a great score in GMAT which would more be like 700+. First of all you have to look whether the colleges you are gonna apply will take GRE score or not. If they do you have to check how many people apply with GRE score and how many apply with GMAT scores and their respective intake percentages.
IMO GRE is a tad easier than GMAT, so with your experience with GMAT will certainly help you for prepping for GRE and maybe 1 month is enough for that. I gave GRE myself on a 30 day prep time and scored 326 (Q-165 , V-161) on my first attempt.

So i would recommend you to take the practice POWERPREP GRE test from ETS and check how much you score , get a feel for it and then decide whether you are confident in scoring a 320+ in GRE.

Go to this following link and download the powerprep and give a mock GRE to test your skills on a new battlefield.
ETS GRE Mock Test(Official)

Best of luck my friend!