Description

A careless student accidentally knocked over the dishwashing uncle's basket in the cafeteria, and chopsticks fell all over the floor.
The uncle got angry and insisted that the student pair up all the chopsticks. Each chopstick has a length, and only chopsticks of the same length can form a pair. However, the uncle told him that there is exactly one chopstick that is unpaired. Can you help the student find the length of the unpaired chopstick?

Input Format

The first line contains a positive integer $N$, representing the number of chopsticks ($1≤N≤5,000,000$).
The next line contains $N$ positive integers, representing the lengths $L_i$ ($1≤L_i≤2,147,483,647$) of each chopstick. There may be many chopsticks of the same length.

Output Format

Output the length of the unpaired chopstick.

Sample

5
1 2 1 2 3

3