#include<iostream>
#include<fstream>

#define INPUT "input.txt"
#define OUTPUT "output.txt"

using namespace std;

struct Symbol
{
    char ch;
    Symbol* next = NULL;
};

bool check(Symbol* firstSymbol)
{
    bool dlt = false;
    Symbol* nowSymbol = firstSymbol, * buf;
    while (nowSymbol->next != NULL)
    {
        if (nowSymbol->next->ch == firstSymbol->ch)
        {
            dlt = true;
            buf = nowSymbol->next->next;
            delete(nowSymbol->next);
            nowSymbol->next = buf;
        }
        else
            nowSymbol = nowSymbol->next;
    }
    return dlt;
}


void main()
{
    char ch;
    bool empty = true;

    fstream file;
    file.open(INPUT);

    if (file.is_open())
    {
        Symbol* firstSymbol = new Symbol, * nowSymbol = firstSymbol, *buf;
        while (!file.eof())
        {
            ch = file.get();
            if ((ch != ' ') && (ch != EOF))
            {
                cout << ch << "\n";
                nowSymbol->next = new Symbol;
                nowSymbol = nowSymbol->next;
                nowSymbol->ch = ch;
                empty = false;
            }
        }
        if (empty != true)
        {
            cout << "_____________ \n";

            file.close();

            file.open(OUTPUT, ios_base::out | ios_base::trunc);
            if (file.is_open())
            {
                nowSymbol = firstSymbol;
                while (nowSymbol->next != NULL)
                {
                    if (check(nowSymbol->next))
                    {
                        buf = nowSymbol->next->next;
                        delete(nowSymbol->next);
                        nowSymbol->next = buf;
                    }
                    else
                    {
                        cout << nowSymbol->next->ch << "\n";
                        file << nowSymbol->next->ch << " ";
                        nowSymbol = nowSymbol->next;
                    }
                }
                file.close();
            }
            else
            {
                cout << "Output file not found!\n";
            }
        }
        else
            cout << "File is empty!\n";
    }
    else {

        cout << "Input file not found!\n";

    }
    cin >> ch;

}