Area of a circle, with default integer value

Question

static void Main(string[] args)
{
    WriteLine("What is the radius of your circle: ");
    WriteLine("The area of your circle is: " + circleArea(Double.Parse(ReadLine())).ToString());
    ReadKey();
}
static double circleArea(double radius = 5.00)
{
    return Math.PI * (radius * radius);
}

So far the code I have is working and it is able to calculate the area of a circle; however, I need to have the main method pass an integer variable (radius) with an optional default value. I thought I had it by adding =5 to my second method, but that wasn't it. 

Any help would be appreciated.