using System;

namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            int numF = int.Parse(Console.ReadLine());
            if (numF == 0 || numF == 1)
            {
                Console.WriteLine("1");
            }
            else if (numF == 2)
            {
                Console.WriteLine("2");
            }
            else
            {
                numRevers(numF);
            }
        }
        static void numRevers(int num)
        {
            int first = 1;
            int sec = 2;
            int sumnum = 1;
            for (int i = 2; i < num; i++)
            {
                sumnum = first + sec;
                first = sec;
                sec = sumnum;
            }
            Console.WriteLine(sec);
        }
    }
}