/**
  *  @Author: Pranta Sarker
  *
  */

#include<bits/stdc++.h>

using namespace std;

#define fast ios_base::sync_with_stdio(0)
#define bfast cin.tie(0)
#define outs(x) cout << x << " "
#define outn(x) cout << x << "\n"
#define sf scanf
#define pf printf
#define pfn(x , k) printf(k , x)
#define nl puts("")
#define psb push_back
#define mset(c,v) memset(c , v , sizeof c)
#define loop0(n) for(int i=0; i<n; i++)
#define loop1(n) for(int i=1; i<=n; i++)
#define mpair(x , y) make_pair(x , y)
#define all(x) x.begin(), x.end()
#define pi acos(-1.0)
#define psb push_back
#define clr clear()

typedef unsigned long long ull;
typedef long long LL;
typedef vector<int>vii;
typedef vector<LL>vll;
typedef vector<string>vs;
typedef map<int, int>mpii;
typedef map<string, int>mpsi;
typedef map<char, int>mpci;
typedef map<LL, LL>mpll;

const int mod = 1000007;
const int high = 1002;

int main()
{
	fast;
	int m, p,  d , s;
	while(cin >> p >> d >> m >> s)
	{
		int cnt = 0;

		LL sum = p;

		while(sum <= s)
		{
			p-=d;

			if(p < m)
			{
				p = m;
			}

			sum+=p;
			cnt+=1;

			//cout << "P = " << p << " cnt = " << cnt << " sum = " << sum << "\n";
		}

		outn(cnt);
	}

	return 0;
}