#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
#ifdef LOCAL
	std::ifstream in("in");
	std::cin.rdbuf(in.rdbuf());
#endif

	int m, p, d, s;
	cin >> p >> d >> m >> s;

	int ans = 0;
	while(p <= s){
		ans++;
		s -= p;
		p = max(m, p - d);
	}
	cout << ans << endl;
}