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();
}
}}

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