15. In the following two arithmetic expressions, the same letters represent the same digits, and different letters represent different digits. Then, the value of $A+B+C+D+E=$ $\qquad$
$$
\begin{array}{r}
A B C \\
+\quad D E \\
\hline \mathbf{6 6 4} \\
+\quad E D \\
\hline \mathbf{1 8}
\end{array}
$$
Answer: 16