output_description: Print the maximum possible final value of x in a sequence of operations such
  that S equals T in the end.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      T
attempt: import re
  
  t = input()
  
  x = 0
  s = ""
  
  k = len(t)
  k0 = len(t.replace("0", ""))
  
  iti = [m.start() for m in re.finditer("0", t)]
  # print(iti)
  GU = 0
  KI = 0
  for i in iti:
      if (i + 1) % 2 == 0:
          GU += 1
      else:
          KI += 1
  
  anst = 0
  # print(KI)
  if k0 % 2 == 1:
      anst = (k0 + 1) * (1 + k0) / 4
      # print(anst)
      anst = anst + (k0 + 1) / 2 * GU + (((k0 + 1) / 2) - 1) * KI
      # print(anst)
  else:
      anst = k0 / 2 + k0 * k0 / 4
      anst = anst + ((k0 / 2) + 0) * GU + (k0 / 2) * KI
  
  print(int(anst))
  
problem_description: Statement
  
  Takahashi has an empty string S and a variable x whose initial value is 0.
  
  Also, we have a string T consisting of `0` and `1`.
  
  Now, Takahashi will do the operation with the following two steps |T| times.
  
    * Insert a `0` or a `1` at any position of S of his choice.
    * Then, increment x by the sum of the digits in the odd positions (first, third, fifth, ...) of S. For example, if S is `01101`, the digits in the odd positions are `0`, `1`, `1` from left to right, so x is incremented by 2.
  
  Print the maximum possible final value of x in a sequence of operations such
  that S equals T in the end.
samples: [{"input": "1101", "output": "5\n    \n\nBelow is one sequence of operations that maximizes the final value of x to 5.\n\n  * Insert a `1` at the beginning of S. S becomes `1`, and x is incremented by 1.\n  * Insert a `0` to the immediate right of the first character of S. S becomes `10`, and x is incremented by 1.\n  * Insert a `1` to the immediate right of the second character of S. S becomes `101`, and x is incremented by 2.\n  * Insert a `1` at the beginning of S. S becomes `1101`, and x is incremented by 1.\n\n* * *"}, {"input": "0111101101", "output": "26"}]