\documentclass{beamer}

\useoutertheme[subsection=false]{smoothbars}
\makeatletter
\patchcmd{\slideentry}{\advance\beamer@tempdim by -.05cm}{\advance\beamer@tempdim by\beamer@vboxoffset\advance\beamer@tempdim by\beamer@boxsize\advance\beamer@tempdim by 1.2\pgflinewidth}{}{}
\patchcmd{\slideentry}{\kern\beamer@tempdim}{\advance\beamer@tempdim by 2pt\advance\beamer@tempdim by\wd\beamer@sectionbox\kern\beamer@tempdim}{}{}

\setbeamertemplate{headline}{%
  \pgfuseshading{beamer@barshade}%
  \vskip-6ex%
  \begin{beamercolorbox}[ignorebg,ht=2.25ex,dp=0.25ex]{section in head/foot}
    \insertnavigation{\paperwidth}
  \end{beamercolorbox}%
}%


\makeatother
\usetheme[bigpagenumber]{Flip}

\begin{document}

\section{title}
\subsection{sub}

\begin{frame}
content...
\end{frame}

\begin{frame}
content...
\end{frame}


\end{document}