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public static void main (String [] args) throws IOException
    {
    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String s = reader.readLine();

        ArrayList<Character> Def = new ArrayList<Character>();
        char [] Arr = new char[s.length()];
        s.getChars(0,s.length(), Arr,0);



        for (int i = 0; i < s.length(); i++)
        {
            int counter = 0;
            for (int j = 0; j < s.length(); j++)
            {
                if (Arr[i]==Arr[j])
                {
                    counter++;
                }
            }
            if (counter  == 1 )
            {
                System.out.println(Arr[i]);
            }
        }

    }
}