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) {
        // Return the number of games you can buy
        //20 3 6 80
        if(s<p){
            return 0;
        }
        if(s==p){
            return 1;
        }
        int items = 1;
        int sum = p;
        int itemprice = p;
        while(sum<=s){
           itemprice = itemprice - d;     
           if(itemprice<=m){
               itemprice = m;
           }
           sum += itemprice;
           items += 1;
        }
        return items-1;
    }

    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();
    }
}