#include <bits/stdc++.h>
using namespace std;
long long m,p,s,d,ans;
int main() 
{
    cin>>p>>d>>m>>s;    
     
    while (s>0)
    {
       s=s-p;
        
       if (s<0) break; 
        else if (s==0) 
        {
            cout<<ans+1<<endl;
            return 0;
        }
        ans++; 
        
        
       p=max(m,p-d); 
    }
    
    cout<<ans<<endl;
    
    return 0;
}