Error in generating sweave-tex -> pdf file

Hi,
I created a Sweave file (see below). when I want to convert tex
file generated from it into pdf, I get error message as follows:

 texi2dvi("test.tex", pdf=TRUE)

Error in texi2dvi("test.tex", pdf = TRUE) :
   Running 'texi2dvi' on 'test.tex' failed.
LaTeX errors:
! Undefined control sequence.
l.8 \begin
           {Schunk}

?
! Interruption.
! Interruption.
<to be read again>
                    {
l.8 \begin{
            Schunk}
! Undefined control sequence.
l.9 \begin
           {Sinput}
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
------------------------
test.Rnw

\usepackage{Sweave}
\ documentclass [ a4paper ]{ article }
\ title { Sweave Example 1}
\ begin { document }
\ maketitle

In this example we embed parts of the examples from the
help page into a \ LaTeX {} document :
<<a>>=
y=2
y = y +1
@
which shows that the location parameter of the Ozone
distribution varies significantly from month to month . Finally we
include a boxplot of the data :

\end{ document }