import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;
public class Main{
public static void main(String[] args) { Scanner in = new Scanner(System.in); int n = in.nextInt(); System.out.println(getMinBagNum(n)); } public static int getMinBagNum(int n){ ArrayList<Integer> list = new ArrayList<>(); for(int i=0; i<=n/8; i++){ double x = ((double)(n-8*i)/6); double temp = Math.abs(x-Math.round(x)); if( temp<0.0000000001 ){ list.add(Integer.valueOf( (int)(x+i) )); } } if(list.size()==0){ return -1; } else{ return Collections.min(list).intValue(); } }
}