Add automatic country selection on my site

Hello, I have a job search website [login to view URL] It lets users search jobs based on inputted keywords location and country. There is a default country set for all users and can be changed too. But I want the country filed to change to user's country automatically when the site is opened, this can be done from the users Ip address. There are services which provide API to do this. It just has to be implemented on my site. I want you to use API from [login to view URL] You can use jasonp for this. I want my site to autoselect the country from visitor's IP and also let the user to change the country from the list already provided on the site.