7.00 To Uppercase

using System;
class ParseTags
{
    static void Main()
    {
        string text = Console.ReadLine();
        string modified = string.Empty;
        for (int i = 0; i < text.Length; i++)
        {
            string openTag = "<upcase>";
            string closeTag = "</upcase>";

            int indexOpen = text.IndexOf(openTag, i);
            int indexClose = text.IndexOf(closeTag, i);
            if (i == indexOpen)
            {
                if (indexOpen != -1 && indexClose != -1)
                {
                    for (int j = indexOpen + openTag.Length; j < indexClose; j++)
                    {
                        modified += text[j].ToString().ToUpper();
                    }
                    i += indexClose - indexOpen + closeTag.Length;
                }
            }
            if (i < text.Length)
            {
                modified += text[i];
            }
        }
        Console.WriteLine(modified);
    }
}