Let \(S = \left\{ n \in \mathbb{N} : \begin{pmatrix} 0 & i \\
1 & 0 \end{pmatrix}^n \begin{pmatrix} a & b \\
c & d \end{pmatrix} = \begin{pmatrix} a & b \\
c & d \end{pmatrix}, \forall a, b, c, d \in \mathbb{R} \right\}\), where \(i = \sqrt{-1}\). Then the number of 2-digit numbers in the set S is __________.