#include <math.h>
#include <stdlib.h>
#include <stdio.h>

#define RADIUS 6371.0088

int main(int argc, char**argv)
{
	if (argc < 3) {
		printf("Usage:\n\t%s [coordinate 1] [coordinate 2] ...\n", argv[0]);
		return 1;
	}

	double *lat = calloc(sizeof(double), argc - 1);
	double *lon = calloc(sizeof(double), argc - 1);
	int i;
	for (i = 1; i < argc; ++i) {
		sscanf(argv[i], "%lf,%lf", &lat[i-1], &lon[i-1]);
		if (lat[i-1] < -90 || lat[i-1] > 90 || lon[i-1] < -180 || lon[i-1] > 180 ) {
			printf("Coordinate out of range.\n");
			return 1;
		}

		lat[i-1] *= M_PI / 180;
		lon[i-1] *= M_PI / 180;
	}

	double latdiff, londiff, a, b, c, total;
	for (i = 2; i < argc; ++i ) {
		latdiff = lat[i-1] - lat[i-2];
		londiff = lon[i-1] - lon[i-2];

		a = sin(latdiff / 2);
		b = sin(londiff / 2);
		a *= a;
		a += cos(lat[i-1]) * cos(lat[i-2]) * b * b;
		c = 2 * atan2(sqrt(a), sqrt(1-a));

		total += c * RADIUS;
	}

	printf("Distance: %lf km\n", total);

	free(lat);
	free(lon);

	return 0;
}