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


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