How to change subitem bullets from square to minus in Beamer?

Question

How to change subitem bullets from square to minus in Beamer ? (setbeamertemplate) I'd like a small horizontal line, showing like a minus symbol. Just simple char: -.

I know that there are : triangle, square, and ball.

The question is a new question, and it is different compared to other ones. It is specific to given issue.

\documentclass[bigger]{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{graphicx}



\setbeamertemplate{itemize items}[triangle]
\setbeamercolor{itemize item}{fg=red}  

\setbeamertemplate{itemize subitem}[square]
\setbeamercolor{itemize subitem}{fg=red}

\begin{document}


\begin{frame}{Introduction}
\begin{itemize}
\item 1
\item 2
\item 3
\end{itemize}
\end{frame}

\end{document}

The improved version looks like this but it has issue with page numbering:

\documentclass[12pt,t]{beamer}

\usepackage{url}
\usepackage{hyperref}
\usepackage{graphicx}
\usepackage{grffile}
\usepackage{color}

\usetheme{CambridgeUS}
% %gets rid of bottom navigation bars, then reset with {}
\setbeamertemplate{navigation symbols}{}
\setbeamertemplate{headline}{}{}
\addtobeamertemplate{headline}{}{\textcolor{white}{\rule{\paperwidth}{5pt}}
}

\setbeamertemplate{footline}[frame number]{}
\usebackgroundtemplate{\includegraphics[width=\paperwidth,height=\paperheight]{background.jpg}}


\newcommand{\unititle}[1]{\title{#1}}
\newcommand{\uniauthor}[1]{\author{#1}}
\newcommand{\uniinstitute}[2]{\institute[#1]{#2}}
\newcommand{\unisection}[1]{\frametitle{#1}}
\newcommand{\unimaketitle}[1]{
\begin{frame}
\maketitle
\end{frame}
}

\usepackage{calc}
\newcommand{\unifig}[2]{
\begin{center}
\hspace{-1cm}\includegraphics[width=#2\textwidth*\real{0.91},keepaspectratio]{#1}
\end{center}
}




\usepackage{xparse,calc}
\newlength\fitimageht
\newlength\fitotherht
\newsavebox\fitimagebox
\NewDocumentCommand \fitimage { m m O {} }{%
  \sbox\fitimagebox{%
     \parbox{\textwidth}{%
       #1\par
       #3
    }%
  }%
  \settototalheight{\fitotherht}{%
     \usebox\fitimagebox
  }%
  \setlength\fitimageht{\textheight}%
  \addtolength\fitimageht{-\fitotherht-\topskip-\footskip-3\baselineskip}%
  #1\par
   \centering
   \includegraphics[width=\textwidth,height=\fitimageht,keepaspectratio]{#2}\par
  #3}

\definecolor{UniRed}{RGB}{204,0,0}
\setbeamertemplate{itemize item}{$>$}
\setbeamercolor{itemize item}{fg=MyMadrid}
\setbeamertemplate{itemize subitem}{$-$}
\setbeamercolor{itemize subitem}{fg=MyMadrid}


\begin{document}

\section{Section}
\begin{frame}
\frametitle{\thesection.~\insertsection}
\begin{itemize}
\item Header
\begin{itemize}
\item this is an example
\end{itemize}
\end{itemize}
\end{frame}


\section{Section Two}
\begin{frame}
\frametitle{\thesection.~\insertsection}
\begin{itemize}
\item Header
\item Header
\item Header
\item Header
\begin{itemize}
\item this is an example
\bigskip
\end{itemize}
\item Header
\begin{itemize}
\item this is an example
\end{itemize}
\end{itemize}
\end{frame}



\end{document}

The improved solution isnt still working, because there is a red foot note (page numbering) :( + TexMaker under Windows gives "beamerbasemodes.sty not found" !