# include <bits/stdc++.h>

using namespace std;

int main()
{
  int p,d,m,s,sum;
  cin>>p>>d>>m>>s;
  if(s<p)
   cout<<"0";
  else
  {
    sum = p;
    int i,cost;
    for(i=1,cost = p-d;;)
    {
      if(cost<m)
       cost = m;
      sum += cost;
      if(sum<=s)
        i++;
      else
        break;
      cost-=d;
    }
    cout<<i;
  }

  return 0;
}