/*
*/

#pragma GCC optimize("O3")
#define _CRT_SECURE_NO_WARNINGS
#include <fstream>
#include <iostream>
#include <string>
#include <complex>
#include <math.h>
#include <set>
#include <vector>
#include <map>
#include <queue>
#include <stdio.h>
#include <stack>
#include <algorithm>
#include <list>
#include <ctime>

#include <memory.h>
#include <assert.h>

#define y0 sdkfaslhagaklsldk

#define y1 aasdfasdfasdf
#define yn askfhwqriuperikldjk
#define j1 assdgsdgasghsf
#define tm sdfjahlfasfh
#define lr asgasgash
#define norm asdfasdgasdgsd
#define have adsgagshdshfhds
#define ends asdgahhfdsfshdshfd

#define eps 1e-11
#define M_PI 3.141592653589793
#define bsize 512

#define ldouble long double
using namespace std;

#define bs 1000000007

const int N = 500031;

int p,d,m,s,ans;

int main(){
	//freopen("tree.in","r",stdin);
	//freopen("tree.out","w",stdout);
	//freopen("input.txt", "r", stdin);
	//freopen("out.txt", "w", stdout);
	ios_base::sync_with_stdio(0);
	//cin.tie(0);

	cin>>p>>d>>m>>s;
	while (true)
	{
		if (p>s)
			break;
		s-=p;
		ans++;
		p-=d;
		if (p<m)
			p=m;
	}
	cout<<ans<<endl;

	cin.get(); cin.get();
	return 0;
}