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 ContestEd54;

import java.io.*;
import java.util.StringTokenizer;

public class mainB {
    public static PrintWriter out = new PrintWriter(System.out);
    public static FastScanner enter = new FastScanner(System.in);

    public static void main(String[] args) throws IOException {
        long n=enter.nextLong();
        long min_val=find_min(n);
        if(min_val==2){
            System.out.println(func(n));
        }
        else{
            System.out.println(1+func(n-min_val));
        }

    }

    public static long func(long n){
        return n/2;
    }

    public static long find_min(long n){
        for (long i = 2; i*i <=n ; i++) {
            if(n%i==0) return i;
        }
        return n;
    }



    static class FastScanner {
        BufferedReader br;
        StringTokenizer stok;

        FastScanner(InputStream is) {
            br = new BufferedReader(new InputStreamReader(is));
        }

        String next() throws IOException {
            while (stok == null || !stok.hasMoreTokens()) {
                String s = br.readLine();
                if (s == null) {
                    return null;
                }
                stok = new StringTokenizer(s);
            }
            return stok.nextToken();
        }

        int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        long nextLong() throws IOException {
            return Long.parseLong(next());
        }

        double nextDouble() throws IOException {
            return Double.parseDouble(next());
        }

        char nextChar() throws IOException {
            return (char) (br.read());
        }

        String nextLine() throws IOException {
            return br.readLine();
        }
    }
}
