For the block matrix $M = \begin{pmatrix} A & B \\ C & D \end{pmatrix} = \begin{pmatrix} 2 & 1 & 1 \\ 0 & 1 & 2 \\ 0 & 3 & 4 \end{pmatrix}$ where $A = (2)$ (scalar), $B = \begin{pmatrix} 1 & 1 \end{pmatrix}$, $C = \begin{pmatrix} 0 \\ 0 \end{pmatrix}$, and $D = \begin{pmatrix} 1 & 2 \\ 3 & 4 \end{pmatrix}$, compute the Schur complement $S = D - CA^{-1}B$.