\documentclass{beamer}
\usepackage[english]{babel}
\usepackage{fancyhdr}        % header footer
\usepackage{graphicx}        % figure
\usepackage{booktabs}
\usepackage{xcolor}
\usepackage{bookmark}
\usepackage{hyperref}
\usepackage{graphicx} % Allows including images
\usepackage{booktabs} % Allows the use of \toprule, \midrule and \bottomrule in tables
\usepackage{tikz}
\usepackage[ruled,linesnumbered]{algorithm2e}
\usepackage{adjustbox}

\author{Yu Cong}
\title{Reachability and Büchi games}
\date{\today}

% \AtBeginSection[]{
%     \frame{\frametitle{Outline}\tableofcontents[currentsection, 
%     subsectionstyle=show/show/shaded]}
% }
    
\usetheme{Simple}
% \useoutertheme{tree}
    
\begin{document}
    \begin{frame}[plain]
        % Print the title page as the first slide
        \titlepage
    \end{frame}

    \begin{frame}[plain]{Overview}
        % Throughout your presentation, if you choose to use \section{} and \subsection{} commands, these will automatically be printed on this slide as an overview of your presentation
        \tableofcontents
    \end{frame}
    \input{content.tex}
\end{document}