#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <iostream>
#include <sstream>
#include <string>
#include <cstring>
#include <map>
#include <set>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <utility>
#include <algorithm>
#include <cassert>

using namespace std;

typedef long long int LLI;
typedef pair<int,int> PII;

#define _ ios_base::sync_with_stdio(0);
#define debug
#define x first
#define y second
#define MXN 100005

const int inf = 0x3f3f3f3f;
const int mod = 1e9+7;
const double eps = 1e-8; 


int main() { _
    int p, d, m, s;
    cin >> p >> d >> m >> s;
    int cnt = 0, cur = 0;
    while (cur < s) {
        cur += p;
        if (cur > s) break;
        ++cnt;
        p = max(p-d, m);
    }
    cout << cnt << "\n";

    return 0;
}