#include <bits/stdc++.h>

using namespace std;

int main(){
	int m, p, d, s;
	cin >> p >> d >> m >> s;
	int ans = 0;
	while(s >= p){
		s -= p;
		p = max(m, p - d);
		ans += 1;
	}
	cout << ans << endl;
	return 0;
}