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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */  
    int p,m,d,s,ans=0;
    cin >> p >> d >> m >> s;
    int n = 1+floor(((p-m)*1.0)/(d*1.0));
    int tot = (n*(2*p-(n-1)*d))/2;
    //cout << tot << endl;
    if(tot <= s)
    {
        ans+=n;
        s-=tot;
        int np = m;
        ans += (s/np);
    }
    else
    {
        ans = 0;
        for(int i=1;i<=n;i++)
        {
            ans = i;
            int tot = (i*(2*p-(i-1)*d))/2;
            if(tot>s)
            {
                ans--;
                break;
            }
        }
    }
    cout << ans << endl;
    return 0;
}