using System;

public class Program

{

    public static void Main() {

        double lat1 = 1.2988322;

        double long1 = 103.7738681;

        double lat2 = 1.2942814;

        double long2 = 103.7736419;

        Console.WriteLine(distance(lat1, long1, lat2, long2).ToString());

    }

    public static double distance(double lat1, double lon1, double lat2, double lon2) {

        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;

            dist = dist * 1.609344;

​

            return (dist);

        }

    }

    public static double deg2rad(double deg) {

        return (deg * Math.PI / 180.0);

    }

    public static double rad2deg(double rad) {

        return (rad / Math.PI * 180.0);

    }

}