list free elastic ips from AWS

I have a requirement where i need to filter out the free elastic ip addresses from AWS account that is, list only those which are not bound to any instance.

There are several filters i have seen here : http://ift.tt/1FMKRmW

but not able to figure out how only free elastic ips can be retrieved.

would be very helpful if anyone can give pointers on this.

Thanks a lot ~Yash