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\documentclass{classes/report}

\begin{document}

\pagenumbering{roman}
\subfile{sections/title}
\newpage

\tableofcontents
\clearpage

\pagenumbering{arabic}

\subfile{sections/abstract}
\newpage

\subfile{sections/main_issue}
\newpage

\subfile{sections/references}

\end{document}