#include<bits/stdc++.h>
using namespace std;

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