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.
/*
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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
//package codeforces;

import java.util.ArrayList;
import java.util.Scanner;

/**
 *
 * @author sang
 */
public class DivisorSubstruction {
    public static void main(String[] args){
       Scanner inp = new Scanner(System.in);
       long n = inp.nextLong(), ans = 1;
       for( long i = 2; i*i <= n; i++)
           if( n%i==0){
               ans+=(n-i)/2;
               break;
           }
       System.out.println(ans);
    }
}
