internal class SortedList<T>
{
    private readonly List<T> src;

    public SortedList() => this.src = new List<T>();

    public int Count => src.Count;

    public void Add(T item)
    {
        int insertIndex = src.BinarySearch(item);
        if (insertIndex < 0) insertIndex = ~insertIndex;
        src.Insert(insertIndex, item);
    }

    public T this[int index] => src[index];

    public bool Remove(T item)
    {
        int index = src.BinarySearch(item);
        if (index < 0) return false;
        src.RemoveAt(index);
        return true;
    }
}

public static double Median(SortedList<int> ar)
{
    int n = ar.Count;
    double median = (ar[n / 2] + ar[(n - 1) / 2]) / 2.0;
    return median;
}

public static int ActivityNotifications(int[] expenditure, int d)
{
    int notifications = 0;
    var previousExpenditures = new SortedList<int>();
    for (int i = 0; i < d; i++) //Add initial expenditures
    {
        previousExpenditures.Add(expenditure[i]);
    }
    for (int i = d; i < expenditure.Length; i++)
    {
        if (expenditure[i] >= 2 * Median(previousExpenditures))
        {
            notifications++;
        }
        previousExpenditures.Remove(expenditure[i - d]);
        previousExpenditures.Add(expenditure[i]);
    }
    return notifications;
}