#include<bits/stdc++.h>
#define ll long long
#define vll vector<ll>
#define sll set<ll>
#define mll map<ll,ll>
#define MOD 1000000007
#define fo(i,n) for(i=0;i<n;i++)
#define mp make_pair
#define pb push_back
#define pll pair<ll,ll>
#define vpll vector<pair<ll,ll> >
#define sc(n) scanf(" %lld",&n)
#define sci(n) scanf(" %d",&n)
#define srt(v) sort(v.begin().v.end())
using namespace std;

int main()
{
    ios::sync_with_stdio(false);
    #ifdef UJJWAL_HOME
        freopen("000.txt","r",stdin);
    #endif // UJJWAL_HOME

    ll i,j,k,n,t,p,d,m,s;

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

    ll c=0;
    while(s>0)
    {
        s-=p;
        c++;
        p=max(p-d,m);
    }

    if(s<0)
        c--;

    cout<<c;

    return 0;
}