Rage Quit [C#]

using System;
using System.Linq;
using System.Text;

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

            int index = 0;

            StringBuilder message = new StringBuilder();

            while (index < text.Length)
            {
                string nonDigits = "";
                string digits = "";

                for (int i = 0; i < text.Length; i++)
                {
                    while (!char.IsDigit(text[index]))
                    {
                        nonDigits += text[index];
                        index++;
                    }

                    while (char.IsDigit(text[index]))
                    {
                        digits += text[index];
                        index++;

                        if (index == text.Length)
                        {
                            break;
                        }
                    }

                    int repeatingCount = int.Parse(digits);

                    for (int j = 0; j < repeatingCount; j++)
                    {
                        message.Append(nonDigits);
                    }

                    if (index == text.Length)
                    {
                        break;
                    }

                    nonDigits = "";
                    digits = "";
                }
            }

            string rageMessage = message.ToString();
            int uniqueSymbolsCount = rageMessage.Distinct().Count();

            Console.WriteLine($"Unique symbols used: {uniqueSymbolsCount}");
            Console.WriteLine(rageMessage);
        }
    }
}