I am trying to calculate the perimeter of a circle using method
for some reason I get an error at:

```
   //double p = 2 * Math.PI * r;

```

I am new to using method please help and show me what I did wrong.

```
    static void Main(string[] args)
    {

        double perimeter;
        Console.Write("Enter Perimeter: ");
        double.TryParse(Console.ReadLine(), out perimeter);
        double per = PerimeterOfCircle(perimeter);
        Console.WriteLine("\nPerimeter of Circle = {0}",
            per.ToString("F3"));

        Console.ReadKey();
    }

    static double PerimeterOfCircle(double p)
    {
        double p = 2 * Math.PI * r;
        return p;
    }

```