#include <bits/stdc++.h>
using namespace std;

long long m, p, d, s, ans;

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