In $△ABC$, $AB=AC=24$ and $BC=18$. Points $D$, $E$, and $F$ are on sides $\overline{AB}$, $\overline{BC}$, and $\overline{AC}$, respectively, such that $\overline{DE}$ and $\overline{EF}$ are parallel to $\overline{AC}$ and $\overline{AB}$, respectively. If $AD=10$, what is the length of side $\overline{DE}$?