C# Win App ตั้งค่าเริ่มต้น TextBox กับ Format ยังไงครับ

private void textBox1_KeyUp(object sender, KeyEventArgs e)
{
    if (!string.IsNullOrEmpty(textBox1.Text))
    {
        System.Globalization.CultureInfo culture = new System.Globalization.CultureInfo("en-US");
        int valueBefore = Int32.Parse(textBox1.Text, System.Globalization.NumberStyles.AllowThousands);
        textBox1.Text = String.Format(culture, "{0:N0}", valueBefore);
        textBox1.Select(textBox1.Text.Length, 0);
    }
}

int integerValue = Int32.Parse(textBox1.Text, System.Globalization.NumberStyles.AllowThousands);