\documentclass[11pt,a4paper]{article}
\pagestyle{empty} 
\usepackage[a4paper, top=3cm, bottom=2.5cm, left=4cm, right=4cm]{geometry}
\usepackage[T1]{fontenc}
\usepackage{authblk}
\usepackage{mathptmx}
\usepackage{cite}
\pagenumbering{gobble}
\renewcommand\Authfont{\normalsize}
\renewcommand\Affilfont{\small}
\setlength{\affilsep}{0.3em}
\renewcommand{\refname}{\normalsize References}



\begin{document}


\title{\fontsize{18pt}{18pt}\selectfont   Title of the abstract}

\author[1,*]{\underline{A. Author}}
\author[1,2]{B. Author}
\author[3]{C. Author}
\affil[1]{Affiliation of first author (Institution, City, Country)}
\affil[2]{Affiliation of second author (Institution, City, Country)}
\affil[3]{Affiliation of third author (Institution, City, Country)}
\affil[*]{\textit{address@domain.com}} %change address@domain.com to your address, or delete the line if you don't want to show your e-mail.
\date{} %do not change

\maketitle
\vspace{-2em}


\noindent Replace these instructions here with the text of your abstract. Abstract should be written in English. Each abstract is limited to one A4 page in vertical format. Font should be 11 Times New Roman, single-spaced. At the top of the document, centered, caps and lower case, type the title of the abstract. All authors should be listed on the next line(s) followed by their affiliation(s). Use numbers to indicate the different affiliations of the authors. \underline{Underline} the name of the author who will present at the conference. Asterisk (*) indicates corresponding author. The author list and author affiliation list should be centered.

Start second and next paragraphs of the body of the abstract with a tab. Call out references using command \textbackslash cite e.g., \cite{ref1,ref2} to insert references in the text. Make all references complete bibliographic citations, according to the style specified below. Please do not modify the format of this abstract.

\paragraph{Acknowledgments}
\vspace{-0.5em}
\textit{If you need to acknowledge financial support/grant/research program, and you need this information to appear in the abstract book, it can be done here.}


\vspace{-0.5em}
\begin{thebibliography}{10}
\vspace{-1em}
\setlength{\itemsep}{0pt}
\setlength{\parskip}{0pt} 
\bibitem{ref1} A. Author \textit{et al}., Journal abbreviation Volume, Page (Year).
\bibitem{ref2} B. Author \textit{et al},. Book Title, Publisher, City, (Year).
\end{thebibliography}


\end{document}