According to the Matrix Tree Theorem, the number of spanning trees of a graph is equal to any cofactor of its Laplacian matrix $L$. For a cycle graph $C_4$ on 4 vertices, the Laplacian matrix is: $L = \begin{pmatrix} 2 & -1 & 0 & -1 \\ -1 & 2 & -1 & 0 \\ 0 & -1 & 2 & -1 \\ -1 & 0 & -1 & 2 \end{pmatrix}$ What is the cofactor $C_{11}$ of $L$, which represents the number of spanning trees of $C_4$?