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.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.StringTokenizer;

public class Main {

    static FastReader read;
    static int N = 1000000;
    static boolean prime[] = new boolean[N + 1];

    public static void main(String[] args) throws IOException {
        read = new FastReader();
        long n = read.nextLong();
        //seve
        for (int i = 0; i < N; i++) {
            prime[i] = true;
        }

        for (int p = 2; p * p <= N; p++) {
            // If prime[p] is not changed, then it is a prime 
            if (prime[p] == true) {
                // Update all multiples of p 
                for (int i = p * 2; i <= N; i += p) {
                    prime[i] = false;
                }
            }
        }
        ArrayList<Integer> p = new ArrayList<>();
        for (int i = 2; i <= N; i++) {
            if (prime[i]) {
                p.add(i);
            }
        }
        long steps = 0;

        o:
        while (n > 0) {
            if (n % 2 == 0) {
                steps += n / 2;
                break;
            }
            for (int i = 0; i < p.size(); i++) {
                if (n % p.get(i) == 0) {
                    n -= p.get(i);
                    steps++;
                    continue o;
                }
            }
            n -= n;
            steps++;
        }

        System.out.println(steps);

    }

}

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;
    }
}
