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: def Z():
      return int(input())
  
  
  def ZZ():
      return [int(_) for _ in input().split()]
  
  
  def main():
      T = input()
      output = 0
      n = e = o = 0
      for i in range(len(T)):
          if T[i] == "1":
              n += 1
          if i % 2 == 0 and T[i] == "1":
              o += 1
          if i % 2 == 1 and T[i] == "1":
              e += 1
  
      l = []
      x = y = 0
      for i in range(len(T)):
          if i % 2 == 0 and T[i] == "1":
              x += 1
          if i % 2 == 1 and T[i] == "1":
              y += 1
          if T[i] == "0":
              l.append([o - x, e - y])
  
      for i in range(1, (n + 1) // 2 + 1):
          output += 2 * i
      if n % 2 == 1:
          output -= (n + 1) // 2
  
      for i in range(len(l)):
          e = o - l[i][0] + l[i][1]
          o = e - l[i][1] + l[i][0]
          x = o if i % 2 == 0 else e
          output += x
  
      print(output)
  
      return
  
  
  if __name__ == "__main__":
      main()
  
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"}]