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

public class Main {
    public static void main(String[] args) {
        Task solver = new Task();
        solver.solve();
    }

    static class Task {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        //
        static final int N = (int) 1e6 + 5;
        int sz, primes[] = new int[N];
        boolean p[] = new boolean[N];

        public void solve() {
            sieve();
            long ans = 0, n = in.nextLong();
            while (n > 0) {
                int yay = -1;
                for (int i = 0; i < sz; i++) {
                    if (n % primes[i] == 0) {
                        yay = primes[i];
                        break;
                    }
                }
                if (yay == 2) {
                    ans += (n / 2);
                    n = 0;
                } else {
                    ans++;
                    n -= yay;
                }
            }
            out.println(ans);
            out.close();
        }

        private void sieve() {
            Arrays.fill(p, true);
            p[0] = p[1] = false;
            for (int i = 2 * 2; i <= N; i += 2) {
                p[i] = false;
            }
            for (int i = 3; i * i < N; i += 2) if (p[i]) {
                for (int k = i * i; k < N; k += i) {
                    p[k] = false;
                }
            }
            primes[sz++] = 2;
            for (int i = 3; i < N; i += 2) {
                if (p[i]) {
                    primes[sz++] = i;
                }
            }
        }
    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            // for file IO, replace this with new FileReader ("in.txt")
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

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

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

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

        public String nextLine() {
            try {
                return reader.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return "";
        }
    }
}