The total number of stereoisomers (counting enantiomers and geometric isomers separately) of the compound CH3CH(Cl)CH=CHCH(Cl)CH3 is ______.

The molecule has two stereogenic carbons ($\mathrm{C^*}$ bearing $\mathrm{Cl}$, $\mathrm{CH_3}$, $\mathrm{H}$ and the vinyl carbon) and one stereogenic double bond. Because the two ends are identical, the molecule is symmetric and some combinations coincide. For each geometry of the double bond (E or Z), the centre pairs $(R,R)$ and $(S,S)$ are enantiomers (two isomers), while $(R,S)$ and $(S,R)$ are the same meso compound (one isomer). That gives $3$ per geometry, and $2\times3=6$ in total. A naive $2^3=8$ overcounts because of the symmetry of the molecule.