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-----
12

-----Sample Output-----
1

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

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