#include <iostream>
#include <cmath>

using namespace std;

int howManyGames(int p, int d, int m, int s) {
    if (s < p) return 0;

    int c = (p - m) / d, pre_cost = (p + p - c * d) * (c + 1) / 2;
    if (pre_cost <= s) {
       return c + 1 + (s - pre_cost) / m;
    } else {
        int a = d, b = d - 2 * p, c = 2 * s - 2 * p;
        double res = (-b - sqrt(double(b * b - 4 * a * c))) / double(2 * a);
        return res + 1;
    }
}

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;
}