Question 19
In triangle $ABC,$ $AB = 13,$ $BC = 14,$ and $CA = 15.$ Distinct points $D,$ $E,$ and $F$ lie on segments $BC,$ $CA,$ and $DE,$ respectively, such that $AD \perp BC,$ $DE \perp AC,$ and $AF \perp BF.$ The length of segment $DF$ can be written as $\dfrac{m}{n},$ where $m$ and $n$ are relatively prime positive integers. What is $m + n?$