<image> As shown in the figure, point $$A$$ is a point outside the plane of $$BCD$$, $$AD=BC$$, $$E$$ and $$F$$ are the midpoints of $$AB$$ and $$CD$$, respectively, and $$EF= \dfrac{\sqrt{2}}{2}AD$$. Find the angle between the skew lines $$AD$$ and $$BC$$.