# include <iostream>
# include <cstdlib>

using namespace std;

int main() {

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

  int num_games = 0;

  int curr_price = p;

  while(s >= curr_price) {
    num_games++;
    s -= curr_price;

    curr_price -= d;
    if(curr_price < m) curr_price = m;
  }

  cout << num_games << endl;

  return 0;

}