# include <bits/stdc++.h>
/// my holy template
# define F first    
# define S second
# define mp make_pair
# define pii pair<int,int>         
/// eveything goes according to plan
# define long long long  
# define pb push_back
# define sz(a) (int)(a.size())
/// countdown BEGAN. 10 , 9 , 8 ...
# define y1    Y_U_NO_y1
# define left  Y_U_NO_left
# define right Y_U_NO_right     

const int Mod = (int)1e9 + 7;
const int MX = 1073741822;
const long MXLL = 9223372036854775807;
const int Sz = 1110111;

using namespace std;

inline void Read_rap () {
  ios_base :: sync_with_stdio(0);
  cin.tie(0); cout.tie(0);
}
inline void randomizer3000 () {
  unsigned int seed;
  asm("rdtsc" : "=A"(seed));
  srand(seed);
}
int p, d, m, s;

int calc()
{
  int ans = 0;   
  while (s >= p) {
    ans ++;
    s -= p;  
    p = max (m, p - d);
  }
  return ans;
}
                              
int main() 
{
  Read_rap ();
  cin >> p >> d >> m >> s;

  cout << calc();


  return 0;
} 










// Coded by Z...