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

static int __carriage_initialised = 0; /* 1 if initialised */
static int __carriage_nb_cells; /* number of cells */
static int __carriage_goal; /* index of the hidden box */
static int __carriage_open_cost; /* open cost */
static int __carriage_rev_cost; /* reverse cost */
static int __carriage_pos; /* current position */
static int __carriage_dir; /* current direction (-1 or 1) */
static long long int __carriage_cost; /* current total cost */

static void __carriage_msg(long long int score, const char *msg)
{
    if (score < 0) printf("%s\n", msg);
	else printf("Found the prince using %lld coins!\n", score);
    exit(0);
}

static void __carriage_init(void)
{
    if(__carriage_initialised != 0)
        return;
    __carriage_initialised = 1;
    if(scanf("%d%d%d%d", &__carriage_nb_cells, &__carriage_rev_cost,
            &__carriage_open_cost, &__carriage_goal) != 4)
        __carriage_msg(-1, "Invalid input, expecting 4 integers.");
	if (__carriage_goal < 0 || __carriage_goal >= __carriage_nb_cells)
		__carriage_msg(-1, "Invalid prince's castle position.");
	
    __carriage_pos = 0;
    __carriage_dir = 1;
    __carriage_cost = 0;
}

/* returns the number of cells */
int carriage_nb_cells()
{
    __carriage_init();
    return __carriage_nb_cells;
}

/* returns the cost of reversing the direction */
int carriage_reverse_cost()
{
    __carriage_init();
    return __carriage_rev_cost;
}

/* returns the cost of opening a box */
int carriage_open_cost()
{
    __carriage_init();
    return __carriage_open_cost;
}

/* moves the carriage (negative for left, positive for right) */
void carriage_move(int n)
{
    __carriage_init();
    if(n * __carriage_dir < 0)
    {
        __carriage_cost += (long long int)(__carriage_rev_cost);
        __carriage_dir *= -1;
    }
    __carriage_pos += n;
    if(__carriage_pos < 0 || __carriage_pos >= __carriage_nb_cells)
        __carriage_msg(-1, "Move outside valid cells");
}
/* open the box on the current cell, returns -1 if the box you are
 * looking for is on the left, +1 if the box is on the right and
 * the function will exit if the box contains the number. */
int carriage_open()
{
    __carriage_init();
    __carriage_cost += (long long int)(__carriage_open_cost);
    if(__carriage_pos == __carriage_goal)
        __carriage_msg(__carriage_cost, "");
    return __carriage_pos < __carriage_goal ? 1 : -1;
}