[Tex/LaTex] Ovalbox with fixed corner diameter

Question

I wish to use \Ovalbox with a fix corner diameter.
How can it be done?

The problem is when I got a lot of text in the box, the corners run over the text.

Answer 1

Sorry my english is not good enough. You want a fix corner diameter and not a fix width You need \cornersize{.2} perhaps ! Something like this :

\documentclass{scrartcl}
\usepackage{fancybox}
\begin{document}
\cornersize{.2} 
\ovalbox{$x^n + y^n = z^n$}
\ovalbox{\begin{minipage}{6cm}
This is the first paragraph. We shall go over Fermat theorem.
\[ x^n + y^n = z^n \]
\end{minipage}}
\end{document}