Lonely Integer

Source: HackerRank

Version: Phuoc Hung OJ Extended

Problem

You are given an array of $n$ integers. Exactly one value occurs once, while every other value occurs exactly twice.

Find the value that occurs once.

For Chapter 32, the primary solution uses a frequency array over the small value domain.

Input

• The first line contains the odd integer $n$.
• The second line contains $a_1,a_2,\ldots,a_n$.

Output

Print the unique value whose frequency is $1$.

Subtasks

Subtask 1 (20 points): $1\le n\le 9$, $n$ is odd, $0\le a_i\le 20$; exactly one value occurs once and every other value occurs exactly twice.

Subtask 2 (30 points): $1\le n\le 49$, $n$ is odd, $0\le a_i\le 60$; exactly one value occurs once and every other value occurs exactly twice.

Subtask 3 (50 points): $1\le n\le 99$, $n$ is odd, $0\le a_i\le 100$; exactly one value occurs once and every other value occurs exactly twice.

Example

Input

5
0 0 1 2 1

Output

2

Explanation

0 and 1 each occur twice; only 2 occurs once.