#include <bits/stdc++.h>
using namespace std;

int m, p, d, s, res;

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