LaTeX.org

\documentclass[10pt,a4paper,oneside]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\begin{document}
hello world
\end{document}

above is simple code i wrote in latex, on compliing it. I got the error undefined control sequence \Documentclass ...