Problem:
Score : 500 points

Problem 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).

Constraints

0 \leq N \leq 10^{18}

Input

Input is given from Standard Input in the following format:

N

Output

Print the number of trailing zeros in the decimal notation of f(N).

Sample Input 1

12

Sample Output 1

1

f(12) = 12 × 10 × 8 × 6 × 4 × 2 = 46080, which has one trailing zero.

Sample Input 2

5

Sample Output 2

0

f(5) = 5 × 3 × 1 = 15, which has no trailing zeros.

Sample Input 3

1000000000000000000

Sample Output 3

124999999999999995

Solution in Python (3.4.3) (judge verdict: Wrong Answer)

N=int(input())
if N%10==0:
  print(int(N/10))
elif N%10==1:
  print("0")
elif N%10==2:
  print(int((N-2)/10))
elif N%10==3:
  print("0")
elif N%10==4:
  print(int((N-4)/10))
elif N%10==5:
  print("0")
elif N%10==6:
  print(int((N-6)/10))
elif N%10==7:
  print("0")
elif N%10==8:
  print(int((N-8)/10))
else:
  print("0")