using System;
using System.Linq;

namespace Program
{   
    class Program
    {
        static void Main()
        {
            int count = int.Parse(Console.ReadLine());
            int div2 = count / 2;
            long ans = 1;
            for(int count2 = 1; count2 <= div2; count2++)
            {
                int keta = count - count2;
                ans += C(keta, count2);
            }
            Console.WriteLine(ans.ToString());
        }
        static long C(int left,int right)
        {
            double ans = 1;
            for (int loop = 0; loop < right; loop++)
            {
                ans *= (left - loop);
                ans /= (right - loop);
            }
            return (long)Math.Round(ans);
        }
    }
}