#include <bits/stdc++.h>

using namespace std;


int main()
{

  int p, d, m, s;

  cin >> p >> d >> m >>s;

  int cnt =0;

  int ss  = p;
  int tmp = p;

  while(ss<=s)
  {
      tmp = tmp-d;

      if(tmp<=m)
          tmp = m;

      ss += tmp ;

      cnt ++;
  }


   cout << cnt ;
    return 0;
}