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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theabd123:
20180530 16:14:41
THE POWER OF XOR 

incomplet_:
20180418 07:47:36
Don't using cin, cout, even with optimal algorithm this result in TLE 

pratikshit:
20180318 15:31:43
first time used XOR in a problem 

zephyr_96:
20180301 12:28:47
Better add JAVA to your list of unsupported languages. 

ayusofayush:
20180224 11:10:15
this problem teaches you the use of xor(^) operator 

abhijeetgurle:
20180210 05:59:24
Even if you write O(nlogn) solution it will get accepted using fast I/O. 

amankriet:
20180122 13:23:40
Last edit: 20180122 13:24:32 

sanyam19:
20180109 16:03:42
learnt a vry gud concept frm ths Q.... :) 

karthik1997:
20180105 15:51:16
Man , int and xor are enough ! O(1) space is enough ! 

amankumarjha:
20180101 11:27:01
Taught me to use xor and %llu 
Added by:  Efim 
Date:  20101104 
Time limit:  0.134s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ASM64 