#include <bits/stdc++.h>
using namespace std;
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);

	int p,d,m;
	int s;
	int NoGames=0;
	cin>>p>>d>>m>>s;
	int initialSum=p;
	int termToadd = p;
	while(initialSum <= s){
		termToadd -= d;
		if(termToadd <m){
			termToadd = m;
		}
		initialSum += termToadd;
		NoGames++;
	}
	cout<<NoGames;

	return 0;
}