""" unique.py """

# usage: python3 unique.py < input

import string
import sys


def cleanse(text):
    """ get word from text """
    stage = text.strip().casefold()

    if stage == '' or stage.isnumeric():
        return None

    if stage.isalpha():
        return stage

    if stage[0] not in string.ascii_lowercase:
        return cleanse(stage[1:]) if len(stage) > 1 else None

    if stage[-1] not in string.ascii_lowercase:
        return cleanse(stage[:-1]) if len(stage) > 1 else None

    valid = string.ascii_lowercase + '.-—_/’\''
    for i in stage:
        if i not in valid:
            break
    else:
        return stage

    print('ignoring:', stage, file=sys.stderr)
    return None


relative_frequency = {}

with sys.stdin as text_file:
    for line in text_file:
        for chunk in line.split():
            word = cleanse(chunk)
            count = relative_frequency.get(word, 0)
            if count > 0:
                relative_frequency[word] += 1
            else:
                relative_frequency[word] = 1

for word, frequency in relative_frequency.items():
    if frequency == 1:
        print(word)