Back up slides in Latex

 To have back slides in latex and not screw up the slide numbering, do this.
 1. Add these after your \usepackage{} lines, before \begin{document}
  \newcounter{sauvegardeenumi}
  \newcommand{\asuivre}{\setcounter{sauvegardeenumi}{\theenumi}}
  \newcommand{\suite}{\setcounter{enumi}{\thesauvegardeenumi}} 

2. Then, as below.
\begin{frame}

Your last slide...

\end{frame}
% BACK UP SLIDES
\newcounter{finalframe}
\setcounter{finalframe}{\value{framenumber}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}
.
.
.
\end{frame}

\begin{frame}
.
.
.
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\setcounter{framenumber}{\value{finalframe}}
\end{document}