Encryption
Müller had made numerous attempts to catch Stierlitz in the act, but Stierlitz always managed to evade him. One day, as Stierlitz was checking his email, Müller quietly entered and noticed a random string of symbols on the screen.
"Cipher," Müller thought.
"UTF-8," Stierlitz thought.
It is known that Stierlitz encrypts his text using the following method:
He removes all spaces and punctuation marks.
He replaces any sequence of consecutive identical letters with a single instance of that letter.
He then repeatedly inserts pairs of identical letters at random positions within the text.
Your task is to restore the text to its state after the second step. To achieve this, remove all pairs of identical symbols that were added during the third step.
Input
The input consists of a single line containing Stierlitz's cipher, which is made up of lowercase Latin letters. The length of the cipher does not exceed 200000 characters.
Output
Output the restored text.