\documentclass[11pt,a4paper]{report}
\usepackage[top=35mm, bottom=35mm, left=25mm, right=25mm]{geometry}
\usepackage{xepersian}
\begin{document}
$$S=\sum_{i=1}^L \sum_{j=1}^L {$ \niphi $(i,j)} $$
$$\oo$$

\end{document}