/***
20 3 6 85
***/
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
int main()
{
	ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL);
	ll p, d, m, s;
	cin >> p >> d >> m >> s;
	int ans = 0;
	while (p <= s)
	{
		s -= p;
		ans++;
		p -= d;
		if (p <= m)
			p = m;
	}
	cout << ans;
}