#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <map>
#include <list>
#include <algorithm>
#include <cmath>
#include <queue>
#include <iterator>
#include <functional>
#include <numeric>
using namespace std;

#define ll long long
#define forn(i,n)for(i=0;i<n;i++)
#define forc(i,c,n)for(i=c;i<=n;i++)
typedef list<ll> LST;
typedef vector<ll> VEC;
typedef map<ll, ll> MAP;


int main() {
	ifstream fin("Text.txt");
	int i, j, k;
	ll a, b, c, d, t,n,node,p,m,s,ans=0;
	
	cin >> p >> d >> m>> s;
	i = 0;
	while (s>=0) {
		s -= max((p - i*d), m);
		ans++;
        i++;
	}
	cout << ans - 1 << endl;
	return 0;
}