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\documentclass[12pt]{exam}
\usepackage{amsmath,amssymb,pstricks,pstricks-add}
\begin{pspicture}(-12,-2)(5,-2)
\psset{unit=.75cm}
\psaxes[linewidth=1.5pt]{<->}(0,0)(-5,-5)(5,5)[$x$-axis,-90][$y$-axis,180]
\psplot[algebraic,linecolor=red,linewidth=1.5pt,arrows=<->]{0.25}{4}{int(x)} %floor(x), int x also
\end{pspicture}
\end{document}