#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


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