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


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