#include <iostream>
using namespace std;

int main() {
	long long s,p,d,m,i,j,k,count=0;
	cin>>p>>d>>m>>s;
	while(s>=p)
	{s-=p;p-=d;
	if(p<m)
	p=m;
		
		count++;}
	
	
	cout<<count<<endl;
	// your code goes here
	return 0;
}