// Solution by Samkit

import java.util.*;

public class UserMainCode {

    static Scanner sc = new Scanner(System.in);

    public static int minimumMoves(int N){
    	int ans = N;
    	for(int i=2;i*i<=N;i++) {
    		if(N%i==0) {
    			ans = i;
    			break;
    		}
    	}
    	return 1 + ((N-ans)/2);
    }

    public static void main(String[] args) {
    	int N = sc.nextInt();

    	System.out.println(minimumMoves(N));
    }
}