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 a[]=new int[11];
        int i=1,count=0;
        a[0]=p;
        while(p!=m && p>m)
        {
            p=p-d;
            a[i]=p;
            i++;
        }
        a[i]=m;
        int p1=a[0];
        for(int j=i+1;j<11;j++)
        {
            a[j]=m;
        }
        int j=0;
        do
            {
            p1=p1+a[j+1];
            j++;
            count++;
            }while(p1<s);
           
        return count;
        }
        
        
    

    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();
    }
}