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();
    
        int count=-1;
        int cost=0;
        
        while(cost <= s)
        {
            cost=cost+p;
            count++;
            p=p-d;
            
            if(p < m)
                p=m;
            
        }
        
        System.out.println(count);
    }    
}