Itachi Uchiha is the most feared ninja among all ninjas . Akatsuki deciding to attack the Hidden Leaf sends Itachi to destroy the Hidden Leaf. Itachi with the help of his sharingan created multiple illusions of himself creating havoc in hidden leaf. Naruto our hero is unable to tell difference between the illusion itachi and the real Itachi. Using his sage abilities he discovers that all the illusion Itachis occur in pairs reveling that real Itachi is only one. Help Naruto in discovering the real Itachi.

INPUT

The first line of input consists of n , the number of Itachis. following n lines consist an single integer indicating the Itachis.

OUTPUT

output single integer indicating the real Itachi.

CONSTRAINTS 3<=n<=100000