using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string clickId;

        string clickRef = "s554618184127e-uid151515";

​

                const string newPattern = @"(s)(\d*\.?\d+)(e)";

            var newPatternMatches = Regex.Matches(clickRef, newPattern, RegexOptions.IgnoreCase);

         foreach (Match match in newPatternMatches)

                {

                    if (!match.Success)

                    {

                        continue;

                    }

​

                    clickId = match.Groups[2].Value;

​

                    Console.WriteLine(clickId);

                }

    }

}