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 ClassProjects;

import java.util.Scanner;
//import java.math.BigInteger;

public class Sample1 {
    
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long n = sc.nextLong();
		long ret = 0;
		if((n & 1) > 0){
		    boolean sw = false;
		    for(long i = 2 ; i * i <= n ; i++){
		        if(n % i == 0){
		            n -= i;
		            sw = true;
		            break;
		        }
		    }
		    if(sw == false){
		        n = 0;
		    }
		    ret = 1;
		}
		ret += n / 2;
		System.out.println(ret);
	}

	public static int abs(int x){
	    if(x < 0)
	        x = x * -1;
	    return x;
	}
	
	public static int min(int x , int y){
	    if(x < y)
	        return x;
	    return y;
	}
	
	public static int max(int x , int y){
	    if(x > y)
	       return x;
	    return y;
	}
}