#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
   int m,p,d,s;
    int c=0;
    cin>>p>>d>>m>>s;
    int r=0;
    while(r<=s)
    {
        //cout<<c<<" "<<p<<" "<<d<<endl;
       
        
        r=r+p;
     //  cout<<p<<" "<<r<<endl;
        if(r>s)
        {
            break;
        }
        if(p>m)
        {
        p=p-d;
            if(p<m)
           p=m;
        }        
        c++;
    }
    
    cout<<c;
    return 0;
}