#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <algorithm>
#include <vector>
#include <iostream>
#include <limits.h>
#include <math.h>
#include <unordered_map>
#include <assert.h>
using namespace std;

#define ran(i, a, b) for ((i) = (a); (i) < (b); (i)++)
#define rep(i, a) ran ((i), 0, (a))
#define rep1(i, a) ran ((i), 1, (a)+1)
typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef long long ll;
#define _0 first
#define _1 second
#define _pb(x) push_back(x)
#define _mp(x, y) make_pair(x, y)
#if defined(SHIROKO1_LOCAL) && !defined(NDEBUG)
#define DEBUG(...) fprintf(stderr, "[DEBUG] " __VA_ARGS__)
#else
#define DEBUG(...) ((void)0)
#endif



int main()
{
	int p, d, m, s;
	cin >> p >> d >> m >> s;
	int n = 0;
	for (;;) {
		if (p > s)
			break;
		n++;
		s -= p;
		p -= d;
		if (p < m)
			p = m;
	}
	cout << n << endl;
	return 0;
}