\documentclass{article}
\usepackage[affil-it]{authblk}
\usepackage{graphicx}
\usepackage[space]{grffile}
\usepackage{latexsym}
\usepackage{textcomp}
\usepackage{longtable}
\usepackage{tabulary}
\usepackage{booktabs,array,multirow}
\usepackage{amsfonts,amsmath,amssymb}
\providecommand\citet{\cite}
\providecommand\citep{\cite}
\providecommand\citealt{\cite}
\usepackage{url}
\usepackage{hyperref}
\hypersetup{colorlinks=false,pdfborder={0 0 0}}
\usepackage{etoolbox}
\makeatletter
\patchcmd\@combinedblfloats{\box\@outputbox}{\unvbox\@outputbox}{}{%
  \errmessage{\noexpand\@combinedblfloats could not be patched}%
}%
\makeatother
% You can conditionalize code for latexml or normal latex using this.
\newif\iflatexml\latexmlfalse
\AtBeginDocument{\DeclareGraphicsExtensions{.pdf,.PDF,.eps,.EPS,.png,.PNG,.tif,.TIF,.jpg,.JPG,.jpeg,.JPEG}}

\usepackage[utf8]{inputenc}
\usepackage[english]{babel}




\begin{document}

\title{My second test paper}


\author{Alex Bukreev}
\affil{Affiliation not available}



\date{\today}

\maketitle




\textit{This is abstract.} 

\section*{Introduction}
Some word about problem should be there. Some cites like this\cite{Kampas_1977} should be there too.

  
  

\section*{Theory}
What about this paper? No one knows. Only few equations
\begin{equation}
\sum_{n=1}^\infty \frac{z^n}{\sqrt{n!}}|n\rangle = |z\rangle 
\end{equation}\selectlanguage{english}
\begin{figure}[h!]
\begin{center}
\includegraphics[width=0.42\columnwidth]{figures/elstmon/elstmon}
\caption{{Replace this text with your caption%
}}
\end{center}
\end{figure}

And some more
\begin{equation}
\begin{gathered}
E=\sqrt{p^2c^2+m^2c^4}=\\
=mc^2+\frac{p^2}{2m}+o(p^3)
\end{gathered}
\end{equation}
  

\section{Conclusion}
\subsection{First conclusion}
\subsection{Second}
It is all.

\selectlanguage{english}
\FloatBarrier
\bibliographystyle{plain}
\bibliography{bibliography/converted_to_latex.bib%
}

\end{document}

