public class GreatCircle {
    public static void main(String[] args) {
        double x1 = Math.toRadians(Double.parseDouble(args[0]));
        double y1 = Math.toRadians(Double.parseDouble(args[1]));
        double x2 = Math.toRadians(Double.parseDouble(args[2]));
        double y2 = Math.toRadians(Double.parseDouble(args[3]));

        double r = 6371.0;
        double deltax = x2 - x1;
        double deltay = y2 - y1;
        double term1 = Math.pow(Math.sin(deltax / 2), 2);
        double term2 = Math.cos(x1) * Math.cos(x2) * Math.pow(Math.sin(deltay / 2), 2);
        double sqrt = Math.sqrt((term1 + term2));
        double distance = 2 * r * (Math.asin(sqrt));
        Math.toDegrees(distance);
        System.out.println(distance + " kilometers");
    }