OLOLO  Onotole needs your help
Onotole has a lot of pyani. Each pyani has a number, writing on it. Pyanis with equal numbers are indistinguishable. Onotole knows everything, so, he knows that each pyani appeared twice, and only one pyani is unique. He wants to get вздръжни эффект, and he needs the unique pyani. Given the list of pyanis denote which one of them appeared once (it is guaranteed that other pyanis appeared twice). 
Input
First line of input contains number of pyanis N <= 500 000. Next N lines contain a single positive integer 1 <= Pi <= 10^9.
Output
Output one positive integer on pyani, which appeared once.
Example
Input:
3
1
8
1
Output: 8
Onotole has found not optimal AC algorithms, so all solutions will be rejudged. He is watching you.
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Akshay Aradhya:
20150718 22:38:58
@Arnab Fast I/O Not required in C++ 

Akshay Aradhya:
20150718 22:38:25
Funniest Problem Statement Ever. You gotta love Russians and their sense of humour :D 

Piyush Kumar:
20150624 12:00:49
Do not use cin>>. Use scanf. 

Arnab Mitra:
20150520 22:31:10
In case you are doing this question using a sort, please use fast I/O 

[Mayank Pratap]:
20150506 18:27:41
Its good to make progress day by day,learning new things ........Meanwhile I was wondering what Mitch and Francky are talking about :P 
Added by:  Efim 
Date:  20101104 
Time limit:  1s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ASM64 