Trade Comissions

using System;


namespace Trade_Comissions
{
    class Program
    {
        static void Main()
        {
            string city = Console.ReadLine().ToLower();
            double sales = double.Parse(Console.ReadLine());
            double comission = -1;
            bool isCity = city == "sofia" || city == "varna" || city == "plovdiv";

            if (!isCity)
            {
                Console.WriteLine("error");
            }
            if (comission <0)
            {
                Console.WriteLine("error");
            }
                if (city == "sofia")
                {
                    if (0 <= sales && sales <= 500)
                    {
                        comission = 0.05;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }
                    else if (500 <= sales && sales <= 1000)
                    {
                        comission = 0.07;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }

                    else if (1000 <= sales && sales <= 10000)
                    {
                        comission = 0.08;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }
                    else if (sales > 10000)
                    {
                        comission = 0.12;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }
                }

                else if (city == "varna")
                {
                    if (0 <= sales && sales <= 500)
                    {
                        comission = 0.045;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }
                else if (500 <= sales && sales <= 1000)
                    {
                        comission = 0.075;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }
                else if (1000 <= sales && sales <= 10000)
                    {
                        comission = 0.1;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }
                else if (10000 < sales)
                    {
                        comission = 0.13;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }
                }

                else if (city == "plovdiv")
                {
                    if (0 <= sales && sales <= 500)
                    {
                        comission = 0.055;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }
                else if (500 <= sales && sales <= 1000)
                    {
                        comission = 0.08;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }
                else if (1000 <= sales && sales <= 10000)
                    {
                        comission = 0.12;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }
                    else if (10000 < sales)
                    {
                        comission = 0.145;
                        Console.WriteLine("{0:f2}", sales * comission);
                    }

                }
            }
        }
    }