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


int main() 
{
    int p,d,m,s,g=0;
    cin >> p >> d >> m >> s;
    while(s>=p)
    {
        s=s-p;
        p=p-d;
        if(p<=m)
        {
            p=m;
        }
        g++;
    }
    cout<<g;
    return 0;
}