#include <bits/stdc++.h>

using namespace std;


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