output_description: Print the integer Takahashi will get minus the integer Nakahashi will get,
  after repeating the following operation K times. If the absolute value of the
  answer exceeds 10^{18}, print `Unfair` instead.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      A B C K
attempt: da = list(map(int,input().split()))
   
  m = 0
  l = pow(10,18)
    
  if da[3] % 2 == 1:
    k = da[1] -da[0]
  else:
    k = da[0] -da[1]
  
  elif abs(da[0] - da[1]) < l:
    print(da[0] - da[1])
  elif abs(da[0] - da[1]) >= l:
    print("Unfair")
problem_description: Statement
  
  Takahashi, Nakahashi and Hikuhashi have integers A, B and C, respectively.
  After repeating the following operation K times, find the integer Takahashi
  will get minus the integer Nakahashi will get:
  
    * Each of them simultaneously calculate the sum of the integers that the other two people have, then replace his own integer with the result.
  
  However, if the absolute value of the answer exceeds 10^{18}, print `Unfair`
  instead.
samples: [{"input": "1 2 3 1", "output": "1\n    \n\nAfter one operation, Takahashi, Nakahashi and Hikuhashi have 5, 4 and 3,\nrespectively. We should print 5-4=1.\n\n* * *"}, {"input": "2 3 2 0", "output": "-1\n    \n\n* * *"}, {"input": "1000000000 1000000000 1000000000 1000000000000000000", "output": "0"}]