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


int main() {
    int ans = 0, p,d,m,s;
    cin >> p >> d >> m >> s;
    while( s >= p ) {
        s -= p;
        p -= d;
        p = max(p, m);
        ++ans;
    }
    cout << ans <<'\n';
    return 0;
}