RageQuit*-withStringBuilder()

using System;
using System.Text;
using System.Text.RegularExpressions;
using System.Collections.Generic;
using System.Linq;

namespace RageQuit
{
    class Program
    {
        static void Main(string[] args)
        {

            string input = Console.ReadLine().ToUpper();

            Regex regexForSymbolsAndNumber = new Regex(@"(.+?)([0-9]+)");
            MatchCollection matchesSymbolsAndNumbers = regexForSymbolsAndNumber.Matches(input);
            StringBuilder sb = new StringBuilder();
            foreach (Match item in matchesSymbolsAndNumbers)
            {
                string symbols = item.Groups[1].Value;
                string number = item.Groups[2].Value;
                int numberInt = int.Parse(number);
                if (numberInt > 0)
                {
                    for (int i = 0; i < numberInt; i++)
                    {
                        sb.Append(symbols);
                    }
                }
            }

            int numberUniqueSymbols = sb.ToString().Distinct().Count();
            Console.WriteLine($"Unique symbols used: {numberUniqueSymbols}");
            Console.WriteLine(sb);
        }
    }
}