\documentclass{beamer}

\usetheme{Berlin}

\begin{document}

\section{Section 1}
\begin{frame}{Some frame}
  This is a frame
\end{frame}

\begin{frame}{Some frame II}
  This is frame is short, and is meant to conclude the topic of the previous one
\end{frame}

\begin{frame}{A new frame}
  Here I'm discussing something new
\end{frame}

\section{Section 2}
\begin{frame}{Some frame}
  This is a frame
\end{frame}

\begin{frame}{A new frame}
  Here I'm discussing something new
\end{frame}

\end{document}