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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class Main {


    public static void main(String[] args) {
        FastReader f = new FastReader();
        int P = 100001;
        long[] primes = new long[9592];
        int point = 0;
        boolean[] bol = new boolean[P];

        for(int i=2;i<P;i++) {
            if(!bol[i]) {
                primes[point] = i;
                point++;
                for(int j=i+i;j<P;j+=i) {
                    bol[j] = true;
                }
            }
        }


        long n = f.nextLong();
        long ans = 0;
        while (n > 0) {
            if(n % 2 == 0) {
                ans += n / 2;
                break;
            }
            ans++;
            for(int i=0;i<9592;i++) {
                if(primes[i]*primes[i] <= n) {
                    if(n % primes[i] == 0) {
                        n -= primes[i];
                        break;
                    }
                } else {
                    n = 0;
                    break;
                }
                n = 0;
            }
        }


        System.out.println(ans);
    }








    //fast input reader
    static class FastReader
    {
        BufferedReader br;
        StringTokenizer st;

        public FastReader()
        {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next()
        {
            while (st == null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch (IOException e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine()
        {
            String str = "";
            try
            {
                str = br.readLine();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }
}


