#include <bits/stdc++.h>

using namespace std;

int howManyGames(int p, int d, int m, int s) {
    // Return the number of games you can buy
    int n=(p-m+d)/d;
    int ts=(n*(2*p-(n-1)*d))/2;
    if(ts==s)
        return n;
    if(ts<s)
    {
        s-=ts;
        n+=(s/m);
        return n;
    }
    int a=p;
    ts=0;
    int k=0;
    while(ts<=s)
    {
        ts+=a;
        a-=d;
        k++;
        
    }
        
    return k-1;
}

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