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).

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).

Constraints

• $0 \leq N \leq 10^{18}$

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

见题面 Input 部分

见题面 Output 部分