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

def main():

    # sys.stdin=open('input148e.txt')

    n = int(input())
    c = 0

    if n % 2 == 1:
        print(0)
        exit()

    r = 10
    while r <= n:
        c += n / r
        r = r * 5
    print(c) 

if __name__ == '__main__':
    main()

import sys

def main():

    # sys.stdin=open('input148e.txt')

    n = int(input())
    c = 0

    if n % 2 == 1:
        print(0)
        exit()

    r = 10
    while r <= n:
        c += n // r
        r = r * 5
    print(c) 

if __name__ == '__main__':
    main()
