#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 x = 0;
    while (s >= p){
        x++;
        s -= p;
        p = max(p - d, m);
    }
    cout << x;
}