import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static int howManyGames(int p, int d, int m, int s) {
        int noGames = 0;
        int currPrice = p;
        //System.out.println(p);
           //System.out.println(d);
           //System.out.println(currPrice);
        while(currPrice <= s) {
            noGames++;
            s-=currPrice;
            currPrice-=d;
            if (currPrice < m) {
                currPrice = m;
            } 
        }
        return noGames;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int p = in.nextInt();
        int d = in.nextInt();
        int m = in.nextInt();
        int s = in.nextInt();
        int answer = howManyGames(p, d, m, s);
        System.out.println(answer);
        in.close();
    }
}