#include <bits/stdc++.h>

using namespace std;

int main() {
//	freopen("f", "r", stdin);
	int p, d, m, s;
	scanf("%d%d%d%d", &p, &d, &m, &s);
	int cur_cost = p, cnt = 0;
	while (1) {
		if (s - cur_cost < 0)
			break;
		s -= cur_cost;
		cnt++;
		cur_cost -= d;
		if (cur_cost < m)
			cur_cost = m;
	}
	printf("%d\n", cnt);
	return 0;
}