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) {
        int count =0;
        int sum = 0;
        while(sum<s)
        {
            sum = sum+p;
            count++;
            if(p>m)
            {
                
            
            p -=d;
                }
            if(p<=m) p = m;
            
        }
        if(sum==s)
            return count;
        else
            return count-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();
    }
}