Let $[ t ]$ denote the greatest integer $\leq t$. Then $\frac { 2 } { \pi } \int _ { \frac { \pi } { 6 } } ^ { \frac { 5 \pi } { 6 } } ( 8 [ \operatorname { cosec } x ] - 5 [ \cot x ] ) d x$ is equal to $\_\_\_\_$