Answer will be 3 assuming that $\Sigma = \{ a\}$ Or It will be $4$ if $\Sigma \supset \{ a \} $
The language $L = \Sigma^* - \{ \in,a\}$
If $\Sigma = \{ a\}$ then the Minimal DFA would look like the following :
If $\Sigma \supset \{ a \} $ then Minimal DFA will look like the above but with one Dead State extra.