Проблема с кодировкой при чтении текста из файла - C#

private void button1_Click(object sender, EventArgs e)
        {
            Stream myStream = null;
            OpenFileDialog openFileDialog1 = new OpenFileDialog();
 
            openFileDialog1.InitialDirectory = "f:";
            openFileDialog1.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
            openFileDialog1.FilterIndex = 1;
            openFileDialog1.RestoreDirectory = true;
 
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                try
                {
                    if ((myStream = openFileDialog1.OpenFile()) != null)
                    {
                        using (myStream)
                        {
                            richTextBox1.LoadFile(myStream, RichTextBoxStreamType.PlainText);
                        }
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show("Error: Could not read file from disk. Original error: " + ex.Message);
                }
 
            }
        }