output_description: Print the number of trailing zeros in the decimal notation of f(N).
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
attempt: # coding: utf-8
  # Your code here!
  
  import sys
  
  n = int(input())
  
  if n % 2 == 1:
      print(0)
      sys.exit()
  
  if n < 2:
      print(0)
      sys.exit()
  
  l = list()
  # 2 * 5
  l.append(10)
  # 2 * 5 * 5
  l.append(50)
  # 2 * 5 * 5 * 5
  l.append(250)
  # 2 * 5 * 5 * 5 * 5
  l.append(1250)
  # 2 * 5 * 5 * 5 * 5 * 5
  l.append(6250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(31250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(156250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(781250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(3906250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(19531250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(97656250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(488281250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(2441406250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(12207031250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(61035156250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(305175781250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(1525878906250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(7629394531250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(38146972656250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(190734863281250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(953674316406250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(4768371582031250)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(23841857910156200)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(119209289550781000)
  # 2 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5
  l.append(596046447753906000)
  
  result = 0
  for a in l:
      result += n // a
  
  print(result)
  
problem_description: Statement
  
  For an integer n not less than 0, let us define f(n) as follows:
  
    * f(n) = 1 (if n < 2)
    * f(n) = n f(n-2) (if n \geq 2)
  
  Given is an integer N. Find the number of trailing zeros in the decimal
  notation of f(N).
samples: [{"input": "12", "output": "1\n    \n\nf(12) = 12 \u00d7 10 \u00d7 8 \u00d7 6 \u00d7 4 \u00d7 2 = 46080, which has one trailing zero.\n\n* * *"}, {"input": "5", "output": "0\n    \n\nf(5) = 5 \u00d7 3 \u00d7 1 = 15, which has no trailing zeros.\n\n* * *"}, {"input": "1000000000000000000", "output": "124999999999999995"}]