/*input
1 1 1 10000

*/
#include <bits/stdc++.h>

using namespace std;

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

	long long k = 0;

	while (s - p >= 0) {
		s -= p;
		p -= d;
		p = max(p, m);
		k++;
	}

	cout << k;


	return 0;
}