#include <iostream>

using namespace std;

int main()
{
	int p, d, m, s; cin >> p >> d >> m >> s;

	int max = 0;
	int currentCost = p;

	while (s >= currentCost)
	{
		s -= currentCost;
		max++;
		currentCost -= d;

		if (currentCost < m) currentCost = m;
	}

	cout << max << endl;

	return 0;
}