If $\overrightarrow{r}.\overrightarrow{a}=0,\overrightarrow{r}.\overrightarrow{b}=0$ and $\overrightarrow{r}.\overrightarrow{c}=0$ for some non-zero vector $\overrightarrow{r}$,then the value of $\overrightarrow{a}.(\overrightarrow{b}\times\overrightarrow{c})$ is___________.
