Let \( O \) be the origin, and \( M \) and \( N \) be the points on the lines \( \dfrac{x-5}{4}=\dfrac{y-4}{1}=\dfrac{z-5}{3} \) and \( \dfrac{x+8}{12}=\dfrac{y+2}{5}=\dfrac{z-11}{9} \) respectively such that \( MN \) is the shortest distance between the given lines. Then \( \overrightarrow{OM}\cdot\overrightarrow{ON} \) is equal to ________.
