#pragma comment(linker, "/STACK:100000000")
#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>

using namespace std;

#define ll long long 
#define pb push_back
#define ppb pop_back

#define y1 aasdfasdfasdf

const ll N = 1e5 + 10;
const ll mod = 1e9 + 7;
const ll INF = 1e18;
const ll inf = -1e18;
const ll M = 1e6;

ll p, d, m, s, ans;

int main()
{
	cin >> p >> d >> m >> s;
	while (s >= p) {
		s -= p;
		p -= d;
		if (p < m) p = m;
		ans++;
	}
	cout << ans;
	cin.get(), cin.get();
	return 0;
}