#include <bits/stdc++.h>
#define F first
#define S second
using namespace std;

typedef pair<int, int> pii;
typedef long long ll;

int main() {
	int p, d, m, s, i, j;
	cin >> p >> d >> m >> s;
	for(i = 1;  ; ++i) {
		if(s < p)
			break;
		s -= p;
		if(p > m)	p -= d;
		if(p <= m)	p = m;
	}
	cout << i - 1;
	return 0;
}