\documentclass[a4, 12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

% Maths
\usepackage{amsmath}
\usepackage{amssymb}

% SI unit
\usepackage{siunitx}

\begin{document}

Hello world

\newpage

Plop test

\end{document}