5. Given that the area of $\triangle A B C$ is $1, D$ is the midpoint of $B C, E, F$ are on $A C, A B$ respectively, and $S_{\triangle B D F}=$ $\frac{1}{5}, S_{\triangle C D E}=\frac{1}{3}\left(S_{\triangle C D E}\right.$ represents the area of $\triangle C D E$, the same applies below). Then $S_{\triangle D E F}=$ $\qquad$
5. $\frac{4}{15}$