[Xymon] mrtg xymon integration problem

[Pavel Traian]

Hi,
I have installed Xymon server on a CentOS 6 x64.
I wanted to integrate MRTG into it and i got an error.
After i add the below lines: 

# For Xymon integration
WorkDir: /var/lib/xymon/rrd
LogFormat: rrdtool

I get this error:

ERROR: could not find RRDs.pm. Use LibAdd: in mrtg.cfg to help mrtg find RRDs.pm

The problem is that i don't know where to find RRDs.pm. 
Regards.