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

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            long[] ret = new long[n + 1];
            ret[0] = 1;
            ret[1] = 1;
            for (int i = 2; i <= n; i++)
            {
                ret[i] = ret[i - 2] + ret[i - 1];
            }
            Console.WriteLine(ret[n]);
        }
    }
}