\documentclass[12pt]{article}

\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{pst-plot}
\usepackage{color}
\pagestyle{empty}

\begin{document}
\[
C\left(u\right) =
    \frac{1}{\sum_{v \in V}{d\left(u,v\right)}}
\]
\end{document}