using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace yuki0715_B
{
    class Program
    {
        static void Main(string[] args)
        {
            int a = getint();
            int ans = -1;
            if (a <= 14)
            {
                Console.WriteLine(ans);
            }
            else
            {            
                Console.WriteLine(a-7);
            }
        }
        public static string[] getsplit()
        {
            string[] x = Console.ReadLine().Split(' ');
            return x;
        }
        public static int getint()
        {
            int x = int.Parse(Console.ReadLine());
            return x;
        }
    }
}