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.Scanner;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
public class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		long n;
    	Scanner in = new Scanner(System.in);
    	n = in.nextLong();
    	long ans = 0;
    	boolean nPrime = false;
    	long i=3;
    	if (n%2 != 0 ){
        		for(i=3; i*i<n ;i++){
            	if (n%i == 0) {
            	    nPrime = true;
                	break;
            	}
            	
        	}
        	ans++;
        	if (nPrime) n=0;
        	else n-=i;
    	}
    	System.out.println(ans + n/2);
	}
}