#include <bits/stdc++.h>

using namespace std;

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