\documentclass[a4paper,10pt]{article}

\input{common.tex}

\begin{document}
\thispagestyle{empty}
\begin{center}
\vspace*{\fill}
\begin{tikzpicture}[x=1cm,y=1cm]

\grid{18}{26}{gray}

\end{tikzpicture}
\vspace*{\fill}
\end{center}
\end{document}