ToUppercase

using System;
using System.IO;

namespace _07.ToUppercase
{
    class ToUppercase
    {
        static void Main()
        {
            int bufSize = 1024;
            Stream inStream = Console.OpenStandardInput(bufSize);
            Console.SetIn(new StreamReader(inStream, Console.InputEncoding, false, bufSize));

            string text = Console.ReadLine();
            string startUpcase = "<upcase>";
            string endUpcase = "</upcase>";
            int startIndex = 0;
            int endIndex = 0;
            string result = string.Empty;
            while (startIndex != -1 && endIndex != -1)
            {
                startIndex = text.IndexOf(startUpcase);
                endIndex = text.IndexOf(endUpcase);
                if (startIndex != -1 && endIndex != -1)
                {
                    var replaceText = text.Substring(startIndex + startUpcase.Length, endIndex - startIndex - endUpcase.Length + 1);
                    var modifiers = replaceText.ToUpper();
                    result = text.Replace(replaceText, modifiers);
                    result = result.Remove(startIndex, startUpcase.Length);
                    result = result.Remove(startIndex + modifiers.Length, endUpcase.Length);
                    text = result;
                }
            }
            Console.WriteLine(result);
        }
    }
}