#include <bits/stdc++.h>

using namespace std;

int howManyGames(int p, int d, int m, int s) {
    int cur=p,res=0;
    for(int i=1;s>=cur;) {
        ++res;
        s-=cur;
        cur-=d;
        if (cur<m) cur=m;
    }
    return res;
}

int main() {
    int p;
    int d;
    int m;
    int s;
    cin >> p >> d >> m >> s;
    int answer = howManyGames(p, d, m, s);
    cout << answer << endl;
    return 0;
}