#include <iostream>
#include <iomanip>
#include <algorithm>
#include <vector>
#include <string>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cmath>
#include <cstring>
using namespace std;

#define pb push_back
#define fst first
#define snd second

typedef long long ll;
typedef pair<int,int> pii;

const ll MOD=1e9+7;

int main(){
  ios::sync_with_stdio(0);
  cin.tie(0);

  int p,d,m,s;

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

  int sum=0;
  int cur=p;
  int res=0;
  while(sum+cur<=s){
    sum+=cur;
    res++;
    cur=max(cur-d,m);
  }
  cout<<res<<'\n';
  return 0;
}