You are given an integer number $n$. The following algorithm is applied to it:

1. if $n = 0$, then end algorithm;
2. find the smallest prime divisor $d$ of $n$;
3. subtract $d$ from $n$ and go to step $1$.

Determine the number of subtrations the algorithm will make.

Input

The only line contains a single integer $n$ ($2 \le n \le 10^{10}$).

Output

Print a single integer — the number of subtractions the algorithm will make.

见题面 Input 部分

见题面 Output 部分

In the first example $5$ is the smallest prime divisor, thus it gets subtracted right away to make a $0$.

In the second example $2$ is the smallest prime divisor at both steps.