#include <bits/stdc++.h>

using namespace std;

#define D(x) cout << #x << " = " << x << endl

int main() {
    int p, d, m, s, ans = 0;
    cin >> p >> d >> m >> s;
    while(s >= 0) {
        s -= p;
        ans++;
        p -= d;
        if(p <= m) p = m;
    }
    cout << ans - 1 << endl;
    return 0;
}