#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll n,i,b[1010],hz,tj,c[150],hv,tt,hs,p,d,m,s;
int main()
{
	cin>>p>>d>>m>>s;
	while(hz<=s)
	{
		hz=hz+p;
		if(hz>s)
			break;
		hs++;
		//cout<<hz<<"\n";
		p=p-d;
		p=max(p,m);
	}
	cout<<hs<<"\n";
}