Section numbering doesn't appear in the sections?

Question

l'm writing an article. In the table of contents the numbering appears as follow :

1. Section one ............ page 4

But in page four I don't find "1. Section one" but "Section one" not preceded by "1." how do I circumvent that?

\documentclass[a4paper,10pt]{article}
\usepackage[utf8]{inputenc}

% Title Page
\title{}
\author{}


\begin{document}
\maketitle

\begin{abstract}

hi
\end{abstract}
\section{General Introduction}

\section{Search engine}
\subsection{ok}
\subsection{conclusion} 



\end{document}