#include<bits/stdc++.h>
using namespace std;
typedef int64_t ll;
ll p,d,m,s;
int main()
{
	cin>>p>>d>>m>>s;
	ll no=0;
	ll spent=0;
	while(spent+p<=s)
	{
		spent+=p;
		no++;
		p-=d;
		if(p<m)p=m;
	}
	cout<<no<<'\n';
}