#include <bits/stdc++.h>
#define si( x ) scanf("%d", &x)
#define sll( x ) scanf("%I64d", &x)
#define mp make_pair
#define pb push_back
#define ff first
#define ss second
using namespace std;

typedef long long ll;

int p,d,m,s;

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