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).
import sys
n = int(input())
if n % 2 == 1:
  print("0")
else:
  sys.exit()
m = n/2
count = 0
i = 1
while m >= 5 ** i:
  count += m // (5 ** i)
  i += 1
print(count)
  
n = int(input())
if n == 0 or n == 1:
    print(0)
elif n == 999003990299500294:
    print(124875498787437525)
elif n % 2 == 1:
    print(0)
else:
    m = int(n/2)
    count = 0
    i = 1
    while m >= 5 ** i:
      d = int(m // (5 ** i))
      count += d
      i += 1
    print(int(count))