#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 curCost=p;
    
    int ans=0;
    while(s>=curCost){
        
        ans++;
        s-=curCost;
        
        curCost-=d;
        
        curCost=max(curCost,m);
    }
    
    cout << ans;
    return 0;
}