% A complete graph
% Author: Quintin Jean-Noël
% <http://moais.imag.fr/membres/jean-noel.quintin/>
\documentclass[varwidth=true, border=2pt]{standalone}
\usepackage[nomessages]{fp}% http://ctan.org/pkg/fp
\usepackage{tikz}
\usetikzlibrary[topaths]


\begin{document}
    \newcommand\n{5}
    \begin{tikzpicture}
        \node[vertex] (N-0) at (0:0) {};
        \foreach \number in {1,...,\n}{
            \node[vertex] (N-\number) at ({\number*(360/\n)}:5.4cm) {};
        }

        \node[vertex,red] (N-0) at (0,0) {};
        \node[vertex,red] (N-4) at ({4*(360/\n)}:5.4cm) {};

        \draw (N-0) -- (N-1);
        \draw (N-0) -- (N-2);
        \draw (N-0) -- (N-3);
        \draw[green,ultra thick] (N-0) -- (N-4);
        \draw (N-0) -- (N-5);
    \end{tikzpicture}
\end{document}
