Double X problem

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Text;



namespace N_redica

{

    class Program

    {


/**
 * Auto-generated code below aims at helping you parse
 * the standard input according to the problem statement.
 **/



        static void Main(string[] args)
        {
            string LON1 = Console.ReadLine();
            string LAT1 = Console.ReadLine();
            string LON = LON1.Replace(',', '.');
            string LAT = LAT1.Replace(',', '.');
            NumberFormatInfo provider = new NumberFormatInfo();
            provider.NumberDecimalSeparator = ".";
            provider.NumberGroupSeparator = ",";
            double longtitudeA = Convert.ToDouble(LON,provider);
            double latitudeA = Convert.ToDouble(LAT,provider);
          //  Console.WriteLine(longtitudeA);
            int N = int.Parse(Console.ReadLine());
            Dictionary<string, double> defib = new Dictionary<string, double>();
            for (int i = 0; i < N; i++)
            {
                string DEFIB = Console.ReadLine();
                string[] input = DEFIB.Split(";");

                string name = input[1];
                string longt = input[input.Length - 2];
                 LON = longt.Replace(',', '.');
                double longtitudeB = Convert.ToDouble(LON, provider);

                string lat = input[input.Length - 1];
                 LAT = lat.Replace(',', '.');
                double latitudeB = Convert.ToDouble(LAT, provider);

                double x1 = longtitudeB - 0.00000000000000000000000000001 - longtitudeA;
              //  Console.WriteLine(x1);
                double x=x1* Math.Cos((latitudeA - latitudeB) / 2);
                double y = latitudeB - latitudeA;
               // Console.WriteLine(y);
                double distance = Math.Sqrt(x*x + y*y) * 6371.0;
                defib[name] = distance;

            }

            double shortestDistance = double.MaxValue;
            string closestName = "";

            foreach (KeyValuePair<string, double> pair in defib)
            {

                if (pair.Value < shortestDistance)
                {
                    shortestDistance = pair.Value;
                    closestName = pair.Key;
                }
            }



            Console.WriteLine(closestName);
            Console.ReadLine();
        }
    }
}
/*input
3,879483
43,608177
3
1;Maison de la Prevention Sante;6 rue Maguelone 340000 Montpellier;;3,87952263361082;43,6071285339217
2;Hotel de Ville;1 place Georges Freche 34267 Montpellier;;3,89652239197876;43,5987299452849
3;Zoo de Lunaret;50 avenue Agropolis 34090 Mtp;;3,87388031141133;43,6395872778854

output
Maison de la Prevention Sante
*/