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.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.math.BigInteger;

public class Main{
    public static void main(String[] args)throws IOException{
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	PrintWriter out = new PrintWriter(System.out);
	long n = Long.parseLong(br.readLine());
	BigInteger aux = new BigInteger(""+n);
	byte sieve[] = new byte [100001];
	int primos[] = new int[317];
	sieve[0] = 1;
	sieve[1] = 1;
	int cont = 0;
	for(int i = 2; i<=10000;i++){
	    if(sieve[i] == 0 && i*i<=100000){
	 	primos[cont] = i;
	 	cont++;
	 	for(int j = i*i;j<=100000;j+=i){
	 	    sieve[j] = 1;
	 	}
	    }
	}
	if(aux.isProbablePrime(20)){
	    out.println(1);
	}else{
	    int ans = 0;
	    if(n%2==0){
		ans+=n/2;
	    }else{
		ans++;
		n-=3;
		if(n>0){
		    ans+=n/2;
		}
	    }
	    out.println(ans);
	}

	out.close();
    }
}
