Activation Keys

using System;


class Program
{
    static void Main()
    {
        string key = Console.ReadLine();
        string input;
        while ((input = Console.ReadLine()) != "Generate")
        {
            string[] cmd = input.Split(">>>");
            switch (cmd[0])
            {
                case "Contains": Contains(key, cmd[1]); break;
                case "Flip": key = Flip(key, cmd); break;
                case "Slice": key = Slice(key, cmd); break;
            }
        }
        Console.WriteLine($"Your activation key is: {key}");
    }

    private static void Contains(string key, string substring)
    {
        if (key.Contains(substring))
            Console.WriteLine($"{key} contains {substring}");
        else
            Console.WriteLine("Substring not found!");
    }

    private static string Flip(string key, string[] cmd)
    {
        int startIndex = int.Parse(cmd[2]);
        int endIndex = int.Parse(cmd[3]);
        string substring = key.Substring(startIndex, endIndex - startIndex);
        key = key.Remove(startIndex, endIndex - startIndex);

        if (cmd[1] == "Upper")
            substring = substring.ToUpper();
        else if (cmd[1] == "Lower")
            substring = substring.ToLower();

        key = key.Insert(startIndex, substring);
        Console.WriteLine(key);
        return key;
    }

    private static string Slice(string key, string[] cmd)
    {
        int startIndex = int.Parse(cmd[1]);
        int endIndex = int.Parse(cmd[2]);
        key = key.Remove(startIndex, endIndex - startIndex);
        Console.WriteLine(key);
        return key;
    }
}