How to install Nagios 4.0.1 (Monitoring Tool) in ubuntu 13.10 server (Saucy Salamander)

Nagios?? Core??? is an Open Source system and network monitoring application. It watches hosts and services that you specify, alerting you when things go bad and when they get better.Nagios Core was originally designed to run under Linux, although it should work under most other unices as well.