I tried installing cacti by
sudo apt-get install cacti. It displays an error message at the end
Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you haverequested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: cacti: Depends: php5-snmp but it is not going to be installed E: Broken packages
How to resolve this error? As I am a beginner in Ubuntu, please explain steps in detail.