Lonely Number

Statement

You are given an array of n integers, where n is odd. Every value occurs exactly twice, except for one value that occurs exactly once. Find that value. Aim for O(n) time and O(1) extra memory.

Input

The first line has n. The second line has the n integers.

Output

Print the value that occurs once.

Constraints

1 <= n <= 199999, n is odd
|a_i| <= 10^9
Exactly one value occurs once and all the others occur exactly twice.

Example 1

5
4 1 2 1 2

4

The values 1 and 2 each appear twice.

Example 2

1
7

7

A single value is the lonely one.