#include<bits/stdc++.h>
using namespace std;
#define mod 1000000007
#define all(v) v.begin(),v.end()
#define rep(i,a,b) for(i=(ll)a;i<(ll)b;i++)
#define revrep(i,a,b) for(i=(ll)a;i>=(ll)b;i--)
#define strep(it,v) for(it=v.begin();it!=v.end_();++it)
#define ii pair<ll,ll>
#define MP make_pair
#define pb push_back
#define f first
#define se second
#define ll long long int
#define vi vector<ll>
ll modexp(ll a,ll b){ ll res = 1; while(b > 0){  if(b & 1) res = (res * a);  a = (a * a);  b/=2;  }  return res; }
#define rs resize
long long readLI(){  register char c;  for(c = getchar(); !(c>='0' && c<='9'); c = getchar());  register long long a=c-'0';
    for(c = getchar(); c>='0' && c<='9'; c = getchar())
        a = (a<<3)+(a<<1)+c-'0';
    return a;
}
const ll N = 100009;
ll p,d,s,m,cnt;
int main()
{
   std::ios_base::sync_with_stdio(false); cin.tie(NULL);
   cin>>p>>d>>s>>m;
   while(m - p >= 0){
      m -= p;
      cnt++;
      p = max(p - d,s);
   }
   cout<<cnt;
   return 0;
}