/*
#####################################################
# Strive for progress... Not for Success. #
#####################################################
*/

#include <bits/stdc++.h>
using namespace std;

//save time
typedef long long ll;

//for sorting
#define all(a) a.begin(),a.end()


//Constants
#define PI   3.141592653593
#define MOD  1000000007
#define EPS  0.000000001

//loops
#define REP(i,n) 	for(ll i=0;i<(n);++i)
#define FOR(i,a,b) 	for(ll i=(a);i<(b);++i)
#define DFOR(i,a,b) for(ll i=(a);i>=(b);--i)

//vectors
#define vi vector<int>
#define vll vector<ll>
#define vii vector<pair<int,int> >
#define pb 	push_back

//pairs
#define pi pair<int,int>
#define mp make_pair
#define F first
#define S second

//fast I/O
#ifndef _WIN32
#define getchar getchar_unlocked
#define putchar putchar_unlocked
#endif
#define gc getchar
#define pc putchar
#define scan getFoo

//If using cin and cout
#define IOS ios::sync_with_stdio(false)
#define TIE cin.tie(NULL)

//queue
#define qi queue<int>
#define PQ priority_queue

//general
#define E empty()

int main(){
	int p,d,m,s;
	cin>>p>>d>>m>>s;
	int curr = p,ans = 0;
	while(1){
		if(s>=curr){
			s-=curr;
			ans++;
			curr-=d;
			if(curr<m) curr = m;
		}
		else{
			break;
		}
	}
	cout<<ans;
	return 0;
}