CWMO 2011 Problem 2

Let $M$ be a subset of $\{1,2,3... 2011\}$ satisfying the following condition: For any three elements in $M$ , there exist two of them $a$ and $b$ such that $a|b$ or $b|a$ . Determine the maximum value of $|M|$ where $|M|$ denotes the number of elements in $M$