На сторонах \(\displaystyle ES{\small,}\) \(\displaystyle SC{\small,}\) \(\displaystyle CD\) и \(\displaystyle ED\) квадрата \(\displaystyle ESCD\) отметили соответственно точки \(\displaystyle R{\small,}\) \(\displaystyle M{\small,}\) \(\displaystyle F\) и \(\displaystyle N\) так, что \(\displaystyle MN \perp RF{\small.}\) Найдите длину отрезка \(\displaystyle RF{\small,}\) если \(\displaystyle ES=9{\small,}\) \(\displaystyle MN=10{\small.}\)

\(\displaystyle RF=\) [ ]