accessing websites using C#
===

I have a problem here. Assume there's a basic calculator implemented in javascript hosted on a website ( I have googled it and to find an example and found this one: http://www.unitsconverter.net/calculator/ ). What I want to do is make a program that opens this website, enters some value and gets the return value. So, in our website calculator, the program:
- open the website
- enters an operand
- enters an operation
- enters an operand
- retrieve the result
Note: things should be done without the need to show anything to the user ( the browser for example ).

I did some search and found about HttpWebRequest and HttpWebRespond. But I think those can be used to post data to the server, which means, The file I'm sending data to must be php, aspx or jsp. But Javascript is client side. So, I think they are kind of useless to me in this case.

Any help?