#include<bits/stdc++.h>
using namespace std;
#define ll long long
int main()
{
	ll p,d,m,s,c=-1,i=0;
	cin>>p>>d>>m>>s;
	while(s>=0)
	{
		s=s-max(p-d*i,m);
		i++;
		c++;
		
	}
	cout<<c;
	
}