calculus - How to solve $ lim_{ntoinfty} frac {(n!)^frac{1}{n}}{n} $?

I need to find the limit for:

$ \lim_{n\to\infty} \frac {(n!)^\frac{1}{n}}{n} $

I know the answer is $\frac {1}{e}$ but I have no idea how to get that answer.
I'd appreciate some help.