SMO 2014 Junior Round 1 Question 17

In the diagram below, $ABCD$ is a trapezium with $AB\parallel DC$ and $\angle ABC=90^\circ$. Points $E$ and $F$ lie on $AB$ and $BC$ respectively such that $\angle EFD=90^\circ$. If $CD+DF=BC=4$, find the perimeter of $\triangle BFE$.