#include <bits/stdc++.h>

using namespace std;

#define sqr(x) ((x) * (x))
#define pb push_back
#define mp make_pair
#define X first
#define Y second
#define fin(name) freopen(name, "r", stdin)
#define fout(name) freopen(name, "w", stdout)
#define I(x, a) for(auto x : a)
#define F(i, l, r) for(auto i = l; i != r; ++i)
#define DF(i, l, r) for(auto i = l; i != r; --i)
#define clean(a) memset((a),0,sizeof (a))
#define sync ios_base::sync_with_stdio(0);cin.tie(0)
#define all(x) x.begin(),x.end()
#define ret return
#define cont continue
#define brk break
#define ins insert

typedef long long ll;
typedef unsigned long long ull;
typedef long double dbl;
typedef pair <int, int> pii;

const int inf = (int)1e9;
const ll linf = (ll)1e18;
const int mod = (int) 1e9 + 7;
const dbl eps = (dbl) 1e-8;
const int maxn = (int) 1e5 + 5;
const dbl pi = acos(-1);


int main()
{
//    fin("t.in");
    sync;
    int p, d, m, s, k = 0;
    cin >> p >> d >> m >> s;
    while (s >= p)
    {
    	s -= p;
    	++k;
    	p -= d;
    	p = max(m, p);
    }
    cout << k << endl;
    return 0;
}