documentclass[10pt,a4paper,oneside]{article}
usepackage[utf8]{inputenc}
usepackage{amsmath}
usepackage{amsfonts}
usepackage{amssymb}
usepackage{graphicx}
usepackage{lmodern}
usepackage[left=2cm,right=2cm,top=2cm,bottom=2cm]{geometry}
newcommand{prob}[1]{vspace{.5cm}noindenttextbf{textsc{Problem}} $left[#1 right]$}}
begin{document}
section{1}
prob {1} This is problem.

end{document}