14. Given that $A B C-A_{1} B_{1} C_{1}$ is a regular triangular prism, $A B=B C$ $=C A=2, A A_{1}=\sqrt{2}, D$ and $E$ are the midpoints of $A C$ and $B C$ respectively. Then the angle formed by $A_{1} D$ and $C_{1} E$ is $\qquad$ .