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

namespace contest
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            Console.WriteLine(f(N));
        }

        static public int f(int N)
        {
            if (N == 1) return 1;
            if (N == 2) return 2;
            return f(N - 2) + f(N - 1);
        }
    }
}