\documentclass[10pt,b5paper]{article}

\headheight 0pt
\addtolength{\topmargin}{-1cm}
\addtolength{\textheight}{1.8cm}

\usepackage{amsmath,amsthm,amssymb}
\usepackage{graphicx}

\makeatletter
\renewcommand\section{\@startsection {section}{1}{\z@}%
	{-3.5ex \@plus -1ex \@minus -.2ex}%
	{2.3ex \@plus.2ex}%
	{\normalfont\large\bfseries}}
\renewcommand\subsection{\@startsection{subsection}{2}{\z@}%
	{-3.25ex\@plus -1ex \@minus -.2ex}%
	{1.5ex \@plus .2ex}%
	{\normalfont\normalsize\bfseries}}
\let\@afterindentfalse\@afterindenttrue
\@afterindenttrue
\makeatother

\renewcommand{\title}[1]{\begin{center}\Large\bfseries #1 \end{center}}
\renewcommand{\author}[1]{\begin{center} #1 \end{center}}

\usepackage{xcolor}
\usepackage{hyperref}
\hypersetup{
  unicode=true,
  pdfborder={0 0 0},
  pdffitwindow=false,
  pdfstartview={FitH},
  pdfpagelayout={OneColumn},
  pdftitle={ },
  pdfauthor={ },
  pdfsubject={ },
  allcolors=gray,
  colorlinks=true
}

%%% https://www.ctan.org/pkg/cite
\usepackage[noadjust]{cite}
\usepackage[font=small]{caption}


\begin{document}

\title{Your Title}

\author{First Author${}^1$, Second Author${}^2$, Third Author${}^{2,3}$\\[2mm]
${}^1$Institution/Faculty,\\
University/Academy, Country\\
\href{mailto:author1@email.here}{author1@email.here}\\[2mm]
${}^2$Institution/Faculty,\\
University/Academy, Country\\
\href{mailto:author2@email.here}{author2@email.here}\\[2mm]
${}^3$Institution/Faculty,\\
University/Academy, Country\\
\href{mailto:author3@email.here}{author3@email.here}}

\begin{abstract}
Your abstract here. 

{\footnotesize\sl Keywords: ... (optional)}

{\footnotesize\sl MSC2020: ... (optional)}
\end{abstract}

\section{Introduction}

Your text here.

This is a very basic template, in order to get you started.

This is a template for journal Biomath Communications:

\href{https://biomath.math.bas.bg/biomath/index.php/conference}{https://biomath.math.bas.bg/biomath/index.php/conference}



\begin{thebibliography}{99}
\small

\bibitem{article1} \href{https://example.net/}{A. A. Author, B. B. Author, ``Article title'', \textit{Journal}, 12(1):1-20, 2022.}

\bibitem{book1} \href{https://example.net/}{C. C. Author, \textit{Book title}, Publisher, City, 2022.}

\bibitem{chapter1} \href{https://example.net/}{D. D. Author, ``Chapter title'', \textit{Book title}, Publisher, City, 21-40, 2022.}

\end{thebibliography}

\end{document}

