#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef set<int> si;

#define REP(i, a, b) \
    for (int i = (a); i < (b); i++)
#define TRvi(c, it) \
    for (vi::iterator it = (c).begin(); it != (c).end(); it++)
#define TRvii(c, it) \
    for (vii::iterator it = (c).begin(); it != (c).end(); it++)

#define INF 2000000000 // 2e9
#define INFLL 2000000000000000000 // 2e18
#define esp 0.0000000001
#define PI 3.14159265

inline ll GCD(ll a, ll b) {while (b != 0) {ll c = a % b; a = b; b = c;} return a;};
inline ll LCM(ll a, ll b) {return (a / GCD(a,b)) * b;};

priority_queue< ll, vector<ll>, greater<ll> > heap;

int main()
{
    int p, d, m, s;
    cin >> p >> d >> m >> s;
    int res = 0;
    int h = 0;
    while (res + p <= s) {
        res += p;
        h++;
        p -= d;
        if (p < m) p = m;
    }
    cout << h;
    return 0;
}