num_words = 0
    num_diffs = 0

    for line in text:
        new_line = line.split()
        for word in new_line:
            word = clean_up(word)
            num_words += 1
            num_copy = 0
            for other_line in text:
                other_new_line = other_line.split()
                for other_word in other_new_line:
                    other_word = clean_up(other_word)
                    if other_word == word:
                        num_copy += 1
            if num_copy < 2:
                num_diffs += 1
    print num_diffs * 1.0 / num_words