#include <bits/stdc++.h>
using namespace std;

int p, d, m, s, ans=0;

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