#include <bits/stdc++.h>

using namespace std;

int main() {
	int p, d, m, s;
	cin >> p >> d >> m >> s;
	int res = 0, i = 0;
	for(int price = p, left = s; ; left -= price, price -= d) {
		price = max(m, price);
		if(left-price < 0)
			break;
		res += price;
		++i;
	}
	
	cout << i << '\n';
}