StreamRead/Write filename issue.

[Solemn]

in this example:

using (StreamWriter sw = new StreamWriter("D:\\BrugerID.txt", true))

I want the "BrugerID" to be replaced with a variable. The variable should be a user input.

In my perfect dream world the lines should be like this:

string fileNameToWrite = Console.ReadLine();
using (StreamWriter sw = new StreamWriter("D:\\{0}.txt",fileNameToWrite, true))
{
//do something.
}

I can't get my head around the logic here, I'm very new to c# - so how do I make this possible?

[Solemn]

string fileName = Console.ReadLine();
using (StreamWriter sw = new StreamWriter("D:\\" + fileName + ".txt", true))
            {
                sw.WriteLine("LOL");
            }

In my frustration, I answered the question on impulse.
It was awesome and now my problem is solved.