#include <bits/stdc++.h>
using namespace std;
#define  PI atan(1)*4

int main() {
   // freopen("output.txt", "w", stdout);
    ios_base::sync_with_stdio(0);
    int p, d, m, s;
    cin >> p >> d >> m >> s;
    int currentPrice = 0;
    int totalPrice = 0;
    int i = 0;
    for ( i = 0; currentPrice+p <=s;i++)
    {
        currentPrice += p;
        p -= d;
        if (p <= m)p = m;
    }
    cout << i << endl;
    return 0;
}