If $\overrightarrow{A}, \overrightarrow{B}, \overrightarrow{C}$ are three vectors such that $|\overrightarrow{A} | = 4, \; |\overrightarrow{B}| = 5,\; |\overrightarrow{C}|=6$, then $[\overrightarrow{A} - \overrightarrow{B} \; \; \overrightarrow{B} - \overrightarrow{C} \; \; \overrightarrow{C} - \overrightarrow{A} ] $ is equal to :