#include <bits/stdc++.h>

using namespace std;

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