output_description: Print the number of positive integers less than or equal to N that have an odd
  number of digits.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
attempt: N = int(input())
  
  ANS = [0] * 5
  flag = 0
  
  if N < 100000:
      if N < 10000:
          if N < 1000:
              if N < 100:
                  if N < 10:
                      ANS[0] = int(N % 10)
                      flag = flag + 1
                  ANS[1] = 9
                  flag = flag + 1
              ANS[2] = 9 + N - 100 + 1
              flag = flag + 1
          ANS[3] = 909
          flag = flag + 1
      ANS[4] = 9 + 900 + N - 10000 + 1
      flag = flag + 1
  elif N == 100000:
      print(90909)
  
  if flag == 5:
      print(ANS[0])
  if flag == 4:
      print(ANS[1])
  if flag == 3:
      print(ANS[2])
  if flag == 2:
      print(ANS[3])
  if flag == 1:
      print(ANS[4])
  
problem_description: Statement
  
  Given is an integer N. Find the number of positive integers less than or equal
  to N that have an odd number of digits (in base ten without leading zeros).
samples: [{"input": "11", "output": "9\n    \n\nAmong the positive integers less than or equal to 11, nine integers have an\nodd number of digits: 1, 2, \\ldots, 9.\n\n* * *"}, {"input": "136", "output": "46\n    \n\nIn addition to 1, 2, \\ldots, 9, another 37 integers also have an odd number of\ndigits: 100, 101, \\ldots, 136.\n\n* * *"}, {"input": "100000", "output": "90909"}]