using System;
using static System.Console;
namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(ReadLine());

            ulong[] a = new ulong[N + 1];

            a[0] = 1;
            a[1] = 1;

            for (int i = 2; i < N + 1; i++)
            {
                a[i] = a[i - 1] + a[i - 2];
            }

            WriteLine(a[N]);
        }
    }
}