output_description: Print Alice's score minus Bob's score when both players take the optimal
  strategy to maximize their scores.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      a_1 a_2 a_3 ... a_N
attempt: l = sorted(map(int, input().split()))
  print(l[::2] - l[1::2])
  
problem_description: Statement
  
  We have N cards. A number a_i is written on the i-th card.  
  Alice and Bob will play a game using these cards. In this game, Alice and Bob
  alternately take one card. Alice goes first.  
  The game ends when all the cards are taken by the two players, and the score
  of each player is the sum of the numbers written on the cards he/she has
  taken. When both players take the optimal strategy to maximize their scores,
  find Alice's score minus Bob's score.
samples: [{"input": "2\n    3 1", "output": "2\n    \n\nFirst, Alice will take the card with 3. Then, Bob will take the card with 1.\nThe difference of their scores will be 3 \\- 1 = 2.\n\n* * *"}, {"input": "3\n    2 7 4", "output": "5\n    \n\nFirst, Alice will take the card with 7. Then, Bob will take the card with 4.\nLastly, Alice will take the card with 2. The difference of their scores will\nbe 7 \\- 4 \\+ 2 = 5. The difference of their scores will be 3 \\- 1 = 2.\n\n* * *"}, {"input": "4\n    20 18 2 18", "output": "18"}]