#include <bits/stdc++.h>

using namespace std;


int main() {
    int p;
    int d;
    int m;
    int s;
    cin >> p >> d >> m >> s;
    long x,total_items=0,price=p;
    x=(p-m)/d;
    if(s>((x+1)*p-(x*(x+1)*d)/2)){
        total_items=(p-m)/d+1;
        s=s-((x+1)*p-(x*(x+1)*d)/2);
        total_items=total_items+s/m;
        cout<<total_items;
    }
    else{
        while(s>=price){
            total_items++;
            s=s-price;
            price=price-d;
        }
        cout<<total_items;
    }
    return 0;
}