If your router is running NAT, you can get the public IP by connecting to special IP detection pages such as on
broadbandreports using a PC behind the router.
How often does your public IP change? I would recommend to subscribe to a free dynDNS service such as
DynDNS.org Once registered, dns information is updated whenever your public IP changes. From then on, you can reach your public IP using e.g. http://kmoorthy.dyndns.org, or whatever you have chosen.
Some routers (e.g. ZyXEL and others) even incorporate a DynDNS.org client so the router takes care of registering the WAN IP change. If not, you need to run a client on your PC that performs this du
ty. Make sure to select something that correctly works across NAT. It is not useful to register your local private address.
😉Also don't forget to forward any ports that you need on the router. What router model do you have?