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
        int noOfGames=0;
        int totalAmountSpent=0;
        int gameCost=0;
        while(totalAmountSpent < s){
           
            if(noOfGames==0){
                gameCost = p;
            }
            else {
                gameCost = (gameCost -d )>m ?(gameCost-d):m;
            }

            if(totalAmountSpent+gameCost> s){
                break;
            }
            
            totalAmountSpent += gameCost;
            noOfGames++;
        }
        return noOfGames;
    }

    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();
    }
}