import math
import sys
n=int(input())
m=list(map(int,input().split()))
d=dict()
for item  in m:
    if item not in d:
        d[item]=1
    else:
        d[item]=d[item]+1

for item in d.keys():
    if d[item]%2!=0:
        print(item)
        sys.exit()
        

/**************************************************************
	Problem: 1472
	User: admin
	Language: Python
	Result: Accepted
	Time:227 ms
	Memory:34480 kb
****************************************************************/