Whats wrong with my code. i'm getting the following error:

using System;

class Program
{

    static string CheckSpeed(double speed)
    {
        // YOUR CODE HERE
        if (speed>65)
        {
            Console.WriteLine("too fast");
        }
       else if (speed<45)
        {
             Console.WriteLine("too slow");
        }
        else
        {
              Console.WriteLine("speed OK");
        }


    }

    static void Main(string[] args)
    {
        // This should print "too slow".
        Console.WriteLine(CheckSpeed(44));
        // This should print "too fast".
        Console.WriteLine(CheckSpeed(88));
        // This should print "speed OK".
        Console.WriteLine(CheckSpeed(55));
    }

}