#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 nr = 0;
    while(p <= s){
        s -= p;
        ++nr;
        p -= d;
        if(p < m) p = m;
    }
    cout << nr << endl;
    return 0;
}