import java.util.Scanner;
import java.util.StringTokenizer;

public class Solution {
	public static void main(String[] args) {
		Scanner kboard = new Scanner(System.in);
		
		StringTokenizer token = new StringTokenizer(kboard.nextLine());
		
		int p = Integer.parseInt(token.nextToken()), d = Integer.parseInt(token.nextToken()), m = Integer.parseInt(token.nextToken()), s = Integer.parseInt(token.nextToken());
		
		int total = 0;
		while (s > 0 && p > m) {
			s -= p;
			p -= d;
			total += 1;
		}
		
		if (s < 0) {
			total -= 1;
			System.out.println(total);
		} else {
			total += s /m;
			System.out.println(total);
		}
	}
}