#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<int, int> ii;
typedef vector<vector<int>> graph;

int main () {
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    #ifdef LOCAL
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    #else
        #define endl '\n'
    #endif

    int p, d, m, s;
    cin >> p >> d >> m >> s;

    int cur = p, ans = 0;
    while (s - cur >= 0) {
        ++ans;
        s -= cur;
        cur -= d;
        if (cur < m) cur = m;
    }

    cout << ans << endl;
}