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

int main() {

	int d = 0;

	long int left = 0;
	long int center = 0;
	long int right = 0;

	char str[20];
	long int count = 0;

	gets(str);
	d = atoi(str);
	gets(str);
	left = atoi(str);
	gets(str);
	center = atoi(str);
	gets(str);
	right = atoi(str);

	if (d == 0) {
		count = -1;
		printf("%ld", count);
		return 0;
	}

	if (!((center < left && center < right) || (center > left && center > right))) {

		long int lc = left - center;
		long int rc = right - center;

		long int l = abs(lc) / d;
		long int r = abs(rc) / d;
		if (l > r) {
			if (right != 0)
				count = r + 1;
			else
				count = l + 1;
		} else {
			if (left != 0)
				count = l + 1;
			else
				count = r + 1;
		}

	}
	if ((left == 0 && center == 0) || (right == 0 && center == 0))
		count = -1;
	if((left == center) || (center == right) || (left == right))
		center = -1;

	printf("%ld", count);

	return 0;

}