using System;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(distance(32.9697, -96.80322, 29.46786, -98.53506, 'M'));

        Console.WriteLine(distance(32.9697, -96.80322, 29.46786, -98.53506, 'K'));

        Console.WriteLine(distance(32.9697, -96.80322, 29.46786, -98.53506, 'N'));

    }

​

    private static double distance(double lat1, double lon1, double lat2, double lon2, char unit)

    {

        if ((lat1 == lat2) && (lon1 == lon2))

        {

            return 0;

        }

        else

        {

            double theta = lon1 - lon2;

            double dist = Math.Sin(deg2rad(lat1)) * Math.Sin(deg2rad(lat2)) + Math.Cos(deg2rad(lat1)) * Math.Cos(deg2rad(lat2)) * Math.Cos(deg2rad(theta));

            dist = Math.Acos(dist);

            dist = rad2deg(dist);

            dist = dist * 60 * 1.1515;

            if (unit == 'K')

            {

                dist = dist * 1.609344;

            }

            else if (unit == 'N')

            {

                dist = dist * 0.8684;

            }

​

            return (dist);

        }

    }

​

    private static double deg2rad(double deg)

    {

        return (deg * Math.PI / 180.0);

    }

​

    private static double rad2deg(double rad)

    {

        return (rad / Math.PI * 180.0);

    }

}