#include<bits/stdc++.h>

using namespace std;

#define mp make_pair
#define F first
#define S second
#define pb push_back
#define fo(i, n) for(int i = 1; i <= n; ++i)

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

const int N = 200200;
const int mod = 1e9 + 7 ;

int main()
{
	ios::sync_with_stdio(0); cin.tie(0);
	int m,p,d,s;
	int cnt=0;
	cin>>p>>d>>m>>s;
	while(true)
	{
		if(s<p)
			break;
		s-=p;
		p-=d;
		p=max(p,m);
		cnt++;
	}
	cout<<cnt;
	return 0;
}