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

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
    ll p,d,m;
    cin>>p>>d>>m;
    ll s;
    cin>>s;
    ll count=0;
    while(s>0)
   {
   	s=s-p;
   	if(s<0)
   	{
   	   break;
	}
	p=p-d;
   	if(p<=m)
   	{
   	  p=m;	
	}
   	
   	count++;
   }
   cout<<count<<endl;
   
}