Cryptotastic #3

$\begin{array} { l l l } & A & B \\ & C & D \\ + & E & F \\ \hline G & H & I \\ \end{array}$

In the above cryptogram all the letters represent distinct digits from 1 to 9.

If $M$ is the maximum possible value of $\overline{GHI}$ and $N$ is the minimum possible value of $\overline{GHI}$ , then find $M - N$ .

If you're interested try Cryptotastic and Cryptotastic #2 .