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

/* A place for carts to go */

#define MAX_WIDTH 256
#define MAX_HEIGHT 256
static char playfield[MAX_HEIGHT][MAX_WIDTH];

/* Some carts to go in the place */

#define MAX_CARTS 256
static int num_carts = 0;
static struct cart {
	short x;
	short y;
	char dir;
	char turn;
	char under;
	char crashed;
} carts[MAX_CARTS];
static const char cart_symbols[] = ">^<v";
static const char track_symbols[] = "-|-|";
static const char cart_turns[] = "LSR";

/* Sort comparator for carts */

int cartcmp(const void *a, const void *b) {
	const struct cart *cart_a = a, *cart_b = b;
	int result = cart_a->crashed - cart_b->crashed;
	if (!result) result = cart_a->y - cart_b->y;
	if (!result) result = cart_a->x - cart_b->x;
	return result;
}

/* Sort carts */

void sort_carts() {
	qsort(carts, num_carts, sizeof (struct cart), cartcmp);
}

/* A way to look at all that stuff */

void show_playfield() {
	for (char *p = *playfield; *p; p += MAX_WIDTH) {
		printf("%s", p);
	}
	putchar('\n');
}

void show_carts() {
	if (num_carts) {
		for (int i = 0; i < num_carts; i++) {
			struct cart *p = &carts[i];
			if (p->crashed) putchar('!');
			printf("%d,%d%c%c%c ",
				p->x, p->y,
				cart_symbols[p->dir],
				cart_turns[p->turn],
				p->under
			);
		}
		putchar('\n');
	}
}

/* Enough messing about */

#define IO_ERROR 2
#define BAD_INPUT 1

int main(int argc, char *argv[]) {

	struct cart *cart;

	/* Read input map and locate carts */

	{
		FILE *input = fopen(argc > 1? argv[1]: "input.txt", "r");
		int error = IO_ERROR;
		if (input) {
			error = BAD_INPUT;
			for (int row = 0; row < MAX_HEIGHT - 1; row++) {
				char *buf = playfield[row];
				if (fgets(buf, MAX_WIDTH, input)) {
					if (buf[strlen(buf) - 1] != '\n') break;
					char *p = buf;
					while (p = strpbrk(p, cart_symbols)) {
						cart = &carts[num_carts++];
						cart->x = p - buf;
						cart->y = row;
						cart->dir = strchr(cart_symbols, *p++) - cart_symbols;
						cart->turn = 0;
						cart->under = track_symbols[cart->dir];
						cart->crashed = 0;
					}
				}
				else {
					error = 0;
					break;
				}
			}
			fclose(input);
		}
		if (error) return error;
	}

	if (0) show_carts();
	if (0) show_playfield();
	
	/* Update cart locations until crashes have removed all but one */

	while (num_carts > 1) {
		for (cart = carts; cart < carts + num_carts; cart++) {
			const static int cos[] = {1, 0, -1, 0, 1};
			const static int *sin = cos + 1;
			playfield[cart->y][cart->x] = cart->under;
			if (cart->crashed) continue;
			cart->x += cos[cart->dir];
			cart->y += sin[cart->dir];
			cart->under = playfield[cart->y][cart->x];
			switch (cart->under) {
			case '+':
				cart->dir = (cart->dir + 1 - cart->turn) & 3;
				cart->turn = (cart->turn + 1) % 3;
				break;
			case '/':
				cart->dir ^= 1;
				break;
			case '\\':
				cart->dir ^= 3;
				break;
			case '|':
				if (!(cart->dir & 1)) goto crash;
				break;
			case '-':
				if (cart->dir & 1) goto crash;
				break;
			default:
			crash:
				for (struct cart *p = carts + num_carts - 1; p >= carts; p--) {
					if (p->x == cart->x && p->y == cart->y) {
						p->crashed = 1;
						playfield[p->y][p->x] = p->under;
					}
				}
				continue;
			}
			playfield[cart->y][cart->x] = cart_symbols[cart->dir];
		}
		sort_carts();
		if (0) show_carts();
		while (num_carts && carts[num_carts - 1].crashed) num_carts--;
		if (0) show_carts();
		if (0) show_playfield();
		if (0) putchar('\n');
	}

	if (0) show_playfield();
	if (num_carts) printf("%d,%d\n", carts->x, carts->y);
	return 0;
}