For an integer $n$ not less than $0$, let us define $f(n)$ as follows: - $f(n) = 1$ (if $n \lt 2$) - $f(n) = n f(n-2)$ (if $n \geq 2$) Given is an integer $N$. Find the number of trailing zeros in the decimal notation of $f(N)$.

Input is given from Standard Input in the following format: >$N$ #### Constraints - $0 \leq N \leq 10^{18}$

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

***For Sample #1:*** $f(12) = 12 × 10 × 8 × 6 × 4 × 2 = 46080$, which has one trailing zero. ***For Sample #2:*** $f(5) = 5 × 3 × 1 = 15$, which has no trailing zeros.

AtCoder [ABC148E]