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


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