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


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