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


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