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


int main() {
  int m, p;
  int d, s;
  cin >> p >> d;
  cin >> m >> s;
  int c = 0;
  while (p > m && s >= p) {
    s -= p;
    c++;
    p -= d;
  }
  if (p <= m) c += s / m;
  cout << c << endl;

  return 0;
}