SI. 4 Let $f(x)$ be a function such that $f(n)=(n-1) f(n-1)$ and $f(1) \neq 0$.
If $S=\frac{f(R)}{(R-1) f(R-3)}$, find the value of $S$.
$$
\begin{array}{l}
f(n)=(n-1) f(n-1)=(n-1)(n-2) f(n-2)=\ldots \ldots . \\
S=\frac{f(11)}{(11) f(11-3)}=\frac{10 \times 9 \times 8 \times f(8)}{10 \times f(8)}=9 \times 8=72
\end{array}
$$

Remark: Original question:
Let $f(x)$ be a function such that $f(n)=(n-1) f(n-1)$. If $S=\frac{f(R)}{(R-1) f(R-3)}$, find the value of $S$. Note that $S$ is undefined when $f(n)=0$ for some integers $n$.