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

public class Solution {

    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();
        if(s<p)
           System.out.println("0"); 
        else
        {
        int c=1;
        int t=p;
        while(t<s)
        {
            if(p-d<m)
            {
                p=m;
             
            }
            else
            {
                p=p-d;
            }
            t=t+p;
            if(t>s)
                break;
            else
            {
            //System.out.println(p+" "+s  );
            c++;
            }
        }
        System.out.println(c);
        }
    }
}