using System.Text.RegularExpressions;

class RegExSample 
{
  static void Main() 
  {
    string s = "Why Don't You watch <NAME>This is Spinal Tap</NAME> on <DAY>Friday</DAY> or whenever?";
    s = Regex.Replace(s, @"((?<!^)\b[A-Z])(?=[^<>]+<[^\/>][^>]+>)", m => m.Value.ToLower());
    System.Console.WriteLine(s);
  }
}