how to label rows and columns of matrix?

Question

i have a matrix as follows:

\begin{document}
\[
\begin{bmatrix}
& S1 & S2 & S3 & S4 \\
W1 & 0 & 0 & 0 & 0  \\ % inserting body of the table
W2 & 0 & 0 & 0 & 0    
\end{bmatrix}
\]
\end{document}

i want to write labels S1,S2,S3,S4 and W1,W2 outside the brackets instead of inside, any help would be appreciated.