Number of optical isomers $=2^{n}$

where, $n=$ number of asymmetric carbon atoms

$2^{1}=2$

Number of geometrical isomers $=2^{n}$ where, $n=$ number of double bonds $=2^{1}=2$

Hence, total number of stereoisomers = Total optical isomers $4 -$ Total geometrical isomers

$=2+2=4$