#include <bits/stdc++.h>

using namespace std;

int howManyGames(double p, double d, double m, double s) {
    if(s<p)
        return 0;
    double temp=s;
    double x= int((p-m)/d);
    double y=p-x*d;
    double ans=0;
    s=s-(p+y)*(x+1)/2;
    if(s>=0)
    {ans=x+1;}
    else
    { while(temp>p)
    {   ans=ans+1;
        temp=temp-p;
        p=p-d;
    }
     return ans;
    }
            
    //s=s-(p+y)*(x+1)/2;
    ans=ans+int(s/m);
    return ans;
    // Return the number of games you can buy
}

int main() {
    double p;
    double d;
    double m;
    double s;
    cin >> p >> d >> m >> s;
    int answer = howManyGames(p, d, m, s);
    cout << answer << endl;
    return 0;
}