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).
def dobfac(num):
    if num < 0:
        return -1;
    count = 0
    i = 5
    while num / i > 0:
        count += num // i // 2
        i *= 5
    return count

if __name__ == "__main__":
    import sys
    in_str = []
    for line in sys.stdin:
        in_str.append(line)
    dobfac(int(in_str[0]))
def dobfac(num):
    count = 0
    i = 5
    if num % 2:
        print(0)
    else:
        while num / i > 0:
            count += num // i // 2
            i *= 5
        print(count)

if __name__ == "__main__":
    import sys
    in_str = []
    for line in sys.stdin:
        in_str.append(line)
    dobfac(int(in_str[0]))