using System;

namespace ConsoleApp3
{
    class Program
    {
        static void Main(string[] args)
        {

            var x = int.Parse(Console.ReadLine());

            if (x == 2)
            {
                Console.WriteLine(2);
                return;
            }

            switch (x % 2)
            {
                case 0:
                    Console.WriteLine((x - 4) / 2 * 10 + 4);
                    break;
                case 1:
                    Console.WriteLine((x - 3) / 2 * 10 + 5);
                    break;
                default:
                    break;
            }
        }
    }
}