output_description: Print the maximum possible value of B_1 + B_2 + ... + B_N.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      A_1 A_2 ... A_N
attempt: a = int(input())
  lis = list(map(int, input().split()))
  lis = sorted(lis)
  i = 0
  while lis[i] < 0:
      if lis[i] <= 0 and lis[i + 1] >= 0:
          if -1 * lis[i] > lis[i + 1]:
              lis[i], lis[i + 1] = -lis[i], -lis[i + 1]
      elif lis[i] <= 0 and lis[i + 1] <= 0:
          lis[i], lis[i + 1] = -lis[i], -lis[i + 1]
      i += 2
  print(sum(lis))
  
problem_description: Statement
  
  There are N integers, A_1, A_2, ..., A_N, arranged in a row in this order.
  
  You can perform the following operation on this integer sequence any number of
  times:
  
  **Operation** : Choose an integer i satisfying 1 \leq i \leq N-1. Multiply
  both A_i and A_{i+1} by -1.
  
  Let B_1, B_2, ..., B_N be the integer sequence after your operations.
  
  Find the maximum possible value of B_1 + B_2 + ... + B_N.
samples: [{"input": "3\n    -10 5 -4", "output": "19\n    \n\nIf we perform the operation as follows:\n\n  * Choose 1 as i, which changes the sequence to 10, -5, -4.\n  * Choose 2 as i, which changes the sequence to 10, 5, 4.\n\nwe have B_1 = 10, B_2 = 5, B_3 = 4. The sum here, B_1 + B_2 + B_3 = 10 + 5 + 4\n= 19, is the maximum possible result.\n\n* * *"}, {"input": "5\n    10 -4 -8 -11 3", "output": "30\n    \n\n* * *"}, {"input": "11\n    -1000000000 1000000000 -1000000000 1000000000 -1000000000 0 1000000000 -1000000000 1000000000 -1000000000 1000000000", "output": "10000000000\n    \n\nThe output may not fit into a 32-bit integer type."}]