1234

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

namespace ConsoleApplication7
{
    class Program
    {
        static void Main(string[] args)
        {
            int f1 = 1, f2 = 2, n, aux = 0;
            n = Convert.ToInt32(Console.ReadLine());
            for (int i = 2; i <= n; i++)
            {
                aux = f1 + f2;
                f1 = f2;
                f2 = aux;
            }
            Console.WriteLine(aux);
            Console.ReadLine();



        }
    }
}