#include<bits/stdc++.h>
#define ll long long int
using namespace std;
int main()
{
    ll p,d,m,s,cnt=0;
    cin>>p>>d>>m>>s;
    while(s>=p)
    {
        cnt++;
        s-=p;
        p=max(m,p-d);
    }
    cout<<cnt;
}