#include <bits/stdc++.h>

using namespace std;


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