For each positive integer $n$, let
$$y _ { n } = \frac { 1 } { n } ( ( n + 1 ) ( n + 2 ) \cdots ( n + n ) ) ^ { \frac { 1 } { n } }$$
For $x \in \mathbb { R }$, let $[ x ]$ be the greatest integer less than or equal to $x$. If $\lim _ { n \rightarrow \infty } y _ { n } = L$, then the value of $[ L ]$ is $\_\_\_\_$.