#include<bits/stdc++.h>
#include<string>
#define pb push_back
#define ll long long
#define mp make_pair
#define fio ios::sync_with_stdio(false)
#define readi(a) scanf("%d",&a)
#define readli(a) scanf("%lld",&a)
#define puti(a) printf("%d",a)
#define putli(a) printf("%lld",a)
#define nl cout<<"\n"
#define mod 1000000007
using namespace std;
int main()
{
fio;
int p,d,m,s,c=0;
cin>>p>>d>>m>>s;
if(p>s)
{cout<<"0";}
else if(p==s)
{cout<<"1";}
else
{int r=0;
while(r<=s)
{
c++;
r=r+p;
p=p-d;
if(p<=m)
{p=m;}
if(r>s)
{r=r-p;
c--;
break;}
else if(r==s)
{break;}
}
cout<<c;
}

return 0;
}