\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  I_1+I_2+I_3=-2i\int_0^{R}\log{|S(i\omega)|}d\omega+i\ \sum_k2\pi\ {\mathrm Re}\, p_k=0.
\end{equation*}
\end{document}