Key Replacer - Regex Archive

using System;
using System.Text.RegularExpressions;

namespace _05KeyReplacer
{
    class Program
    {
        static void Main(string[] args)
        {
            string key = Console.ReadLine();
            string text = Console.ReadLine();

            string start = string.Empty;

            for (int i = 0; i < key.Length; i++)
            {
                char curr = key[i];

                if (curr == '|' || curr == '\\' || curr == '<')
                {
                    break;
                }
                else if (char.IsLetter(curr))
                {
                    start += curr;
                }
            }

            string reversedEnd = string.Empty;

            for (int i = key.Length - 1; i >= 0; i--)
            {
                char curr = key[i];

                if (curr == '|' || curr == '\\' || curr == '<')
                {
                    break;
                }
                else if (char.IsLetter(curr))
                {
                    reversedEnd += curr;
                }
            }

            string end = string.Empty;

            for (int i = reversedEnd.Length - 1; i >= 0; i--)
            {
                char curr = reversedEnd[i];

                end += curr;
            }

            string pattern = $@"({start}(?<word>.{{0,}}?){end})";

            string result = string.Empty;

            MatchCollection matches = Regex.Matches(text, pattern);

            foreach (Match match in matches)
            {
                string word = match.Groups["word"].Value;

                result += word;
            }

            if (result==string.Empty)
            {
                Console.WriteLine("Empty result");
                return;
            }
            Console.WriteLine(result);
        }
    }
}