import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        int n = in.nextInt();
        in.close();

        int minBags = -1;

        for (int i = 0; i <= n / 6; i++) {
            int remain = n - i * 6;
            if (remain % 8 == 0) {
                int bags = i + remain / 8;
                if (minBags == -1 || bags < minBags) {
                    minBags = bags;
                }
            }
        }
        System.out.println(minBags);
    }
}