#include <bits/stdc++.h>

using namespace std;



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