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 ≤ n ≤ 10^{10}).

Output

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

Examples

Input


5


Output


1


Input


4


Output


2

Note

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.
import java.io.*;
import java.util.*;
public class Ideone {
	public static void main(String[] args) throws IOException {
	Scanner sc=new Scanner(System.in);
		long n = sc.nextLong();
		long c = 0;
		if (n % 2 == 1) {
			c = 1;
			for (int a = 3; (long) a * a <= n; a += 2)
			{
			    if (n % a == 0) {
					n -= a;
					break;
				}
			}
			if(n%2==1)
			n=0;
		}
			
		c += n / 2;
		System.out.println(c);
	}
}