new_contents: N = raw_input()
  #map function apply int() function for all result
  #which return from raw_input
  list = map(int, raw_input().strip().split(" "))
  for i in list: 
  	if(list.count(i) == 1):
  		print i  
  		break;
  
  
  
  
  
subject: Create LonelyInteger.py