\documentclass{book}
\usepackage{subfiles}

\input{./chapters/preamble}

\title{Test file.}
\author{Tester Testington}

\begin{document}
\maketitle

\chapter{Chapter in main}
\subfile{chapters/subfile.tex}

\begin{quote}
  A custom environment.
\end{quote}

\input{./chapters/chapter00}
\input{./chapters/chapter01}
\input{./chapters/chapter02}
\input{./chapters/chapter03}
\input{./chapters/chapter04}
\input{./chapters/chapter05}
\input{./chapters/chapter06}
\input{./chapters/chapter07}
\input{./chapters/chapter08}
\input{./chapters/chapter09}
\input{./chapters/chapter10}
\input{./chapters/chapter11}
\input{./chapters/chapter12}
\input{./chapters/chapter13}
\input{./chapters/chapter14}
\input{./chapters/chapter15}
\input{./chapters/chapter16}
\input{./chapters/chapter17}
\input{./chapters/chapter18}
\input{./chapters/chapter19}
\input{./chapters/chapter20}
\input{./chapters/chapter21}
\input{./chapters/chapter22}
\input{./chapters/chapter23}
\input{./chapters/chapter24}
\input{./chapters/chapter25}
\input{./chapters/chapter26}
\input{./chapters/chapter27}
\input{./chapters/chapter28}
\input{./chapters/chapter29}
\input{./chapters/chapter30}
\input{./chapters/chapter31}
\input{./chapters/chapter32}
\input{./chapters/chapter33}
\input{./chapters/chapter34}
\input{./chapters/chapter35}
\input{./chapters/chapter36}
\input{./chapters/chapter37}
\input{./chapters/chapter38}
\input{./chapters/chapter39}
\input{./chapters/chapter40}
\input{./chapters/chapter41}
\input{./chapters/chapter42}
\input{./chapters/chapter43}
\input{./chapters/chapter44}
\input{./chapters/chapter45}
\input{./chapters/chapter46}
\input{./chapters/chapter47}
\input{./chapters/chapter48}
\input{./chapters/chapter49}
\input{./chapters/chapter50}
\input{./chapters/chapter51}
\input{./chapters/chapter52}
\input{./chapters/chapter53}
\input{./chapters/chapter54}
\input{./chapters/chapter55}
\input{./chapters/chapter56}
\input{./chapters/chapter57}
\input{./chapters/chapter58}
\input{./chapters/chapter59}
\input{./chapters/chapter60}
\input{./chapters/chapter61}
\input{./chapters/chapter62}
\input{./chapters/chapter63}
\input{./chapters/chapter64}
\input{./chapters/chapter65}
\input{./chapters/chapter66}
\input{./chapters/chapter67}
\input{./chapters/chapter68}
\input{./chapters/chapter69}
\input{./chapters/chapter70}
\input{./chapters/chapter71}
\input{./chapters/chapter72}
\input{./chapters/chapter73}
\input{./chapters/chapter74}
\input{./chapters/chapter75}
\input{./chapters/chapter76}
\input{./chapters/chapter77}
\input{./chapters/chapter78}
\input{./chapters/chapter79}
\input{./chapters/chapter80}
\input{./chapters/chapter81}
\input{./chapters/chapter82}
\input{./chapters/chapter83}
\input{./chapters/chapter84}
\input{./chapters/chapter85}
\input{./chapters/chapter86}
\input{./chapters/chapter87}
\input{./chapters/chapter88}
\input{./chapters/chapter89}
\input{./chapters/chapter90}
\input{./chapters/chapter91}
\input{./chapters/chapter92}
\input{./chapters/chapter93}
\input{./chapters/chapter94}
\input{./chapters/chapter95}
\input{./chapters/chapter96}
\input{./chapters/chapter97}
\input{./chapters/chapter98}
\input{./chapters/chapter99}

\end{document}
