Answers by visitors named: The answer is 669

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Since your friend receives at least $1$ chocolate bar, the maximum number of chocolate bars you can get is $2010 - 1 = 2009$. If you receive $n$ chocolate bars, then your friend gets $2010-n$ chocolate bars. Since you must have at least twice as many chocolate bars as your friend, we have the inequality\begin{align*} n &\ge 2(2010-n) \\ \Rightarrow\qquad n &\ge 4020-2n \\ \Rightarrow\qquad 3n &\ge 4020 \\ \Rightarrow\qquad n &\ge 1340. \end{align*}Therefore, you must keep a minimum of $1340$ chocolate bars. Therefore, the difference between the maximum and minimum number of chocolate bars you can have is $2009 - 1340 = \boxed{669}$.