using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _23UniqueLetters
{
    class UniqueLetters
    {
        static void Main(string[] args)
        {
            string sample = "ala bala nica, ABBA aaaaaataka boobs mississippi";
            StringBuilder sb = new StringBuilder();
            char lastAppended = char.MinValue;

            for (int i = 0; i < sample.Length; i++)
            {
                char currentSymbol = sample[i];
                if (('a' <= currentSymbol || currentSymbol <= 'z') || ('A' <= currentSymbol || currentSymbol <= 'Z'))
                {
                    if (currentSymbol != lastAppended)
                    {
                        sb.Append(currentSymbol);
                        lastAppended = currentSymbol;
                    }
                }
                else
                {
                    sb.Append(currentSymbol);
                }
            }
            Console.WriteLine(sb.ToString());

        }
    }
}