Determine the greatest possible value of n that satisfies the following condition: for any choice of $n$ subsets $M_1, ...,M_n$ of the set $M = \{1,2,...,n\}$ satisfying the conditions i) $i \in M_i$ and ii) $i \in M_j \Leftrightarrow j \notin M_i$ for all $i \ne j$, there exist $M_k$ and $M_l$ such that $M_k \cup M_l = M$. (Moscow regional olympiad,adopted)