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 sum  = 0;
        int i;
       
            for(i =1 ; sum < s ;i++)
            {
                
                 sum += p;
             
                    
                p = p-d;
              if(p <= m)
                  p=m;
                
                //System.out.println(sum + " " +p);
            }
        if(sum > s)
            i = i-1;
        
        return i-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();
    }
}