protected virtual void OnPropertyChanged(string propertyName)
        {
            try
            {
                CurrentPoints.Clear();
                CurrentPoints.Add(new KeyValuePair <double, double>(N * M, N));
                CurrentPoints.Add(new KeyValuePair <double, double>(N * M, M));
            }
            catch (Exception)
            {
            }

            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }