using System;
using System.Text.RegularExpressions;
using System.Collections.Specialized;
class Program
{
static void Main()  {
string s1 = @"want to find this text
<p>I don't want to find this text</p>
I want to find this text";
var myRegex = new Regex(@"(?i)<(\w+).*?<\/\1[^>]*>|([a-z][a-z ]+)");
var group1Caps = new StringCollection();
    
Match matchResult = myRegex.Match(s1);
// put Group 2 captures in a list
while (matchResult.Success) {
   if (matchResult.Groups[2].Value != "") {
        group1Caps.Add(matchResult.Groups[2].Value);
        }
  matchResult = matchResult.NextMatch();
}

Console.WriteLine("\n" + "*** Matches ***");
if (group1Caps.Count > 0) {
   foreach (string match in group1Caps) Console.WriteLine(match);
   }

Console.WriteLine("\nPress Any Key to Exit.");
Console.ReadKey();

} // END Main
} // END Program