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: L = [
      10,
      50,
      250,
      1250,
      6250,
      31250,
      156250,
      781250,
      3906250,
      19531250,
      97656250,
      488281250,
      2441406250,
      12207031250,
      61035156250,
      305175781250,
      1525878906250,
      7629394531250,
      38146972656250,
      190734863281250,
      953674316406250,
      4768371582031250,
      23841857910156250,
      119209289550781250,
      596046447753906250,
  ]
  N = int(input())
  A = 0
  if N % 2 == 0:
      for i in L:
          A += N // i
  print(A)
  
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"}]