#include<bits/stdc++.h>
#define pb push_back
#define ff first
#define ss second
#define mp make_pair
#define ll long long int
#define mod 1000000007
using namespace std;
int main()
{
  int p,d,m,s,sum=0,tot,count=0;
  cin>>p>>d>>m>>s;
  tot=p;
  if(s<p)
  {
    cout<<0;
    return 0;
  }
  else if(s==p)
  {
    cout<<1;
    return 0;
  }
  int flag=0;
  while(tot>=m)
  {
    sum+=tot;
    if(sum>s)
    { flag=1; break; }
    tot-=d;
    count++;
  }
  if(!flag)
  count+=(s-sum)/m;

  cout<<count;
}