import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long n = scanner.nextLong();
        long ans = 0;
        if (n % 2 == 0) ans = n / 2;
        else  {
            long t = n;
            for (long i = 2; i * i <= n; i++) {
                if (n % i == 0) {
                    t = i;
                    break;
                }
            }

            ans++;
            n -= t;
            ans += n >> 1;
        }

        System.out.println(ans);
    }
}