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.
/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
public class Ideone
{
	static long n;
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		Scanner sc=new Scanner(System.in);
		long c=0;
		n=sc.nextLong();
		long d=prime();
		c=0;
		/*if(d==-1)
		{
			System.out.println(1);
			return;
		}*/
		if(n%2==1)
		{
			n=n-d;
			c++;
			c+=n/2;;
		}
		else
		{
			c+=n/2;
		}
		System.out.println(c);
	}
	static long prime()
	{
		long sq,i;
		//sq=(long)Math.sqrt(n);
		for(i=2;i*i<=n;i++)
		{
			if(n%i==0)
			{
				return i;
			}
		}
		return -1;
		
	}
}