using System;
using System.Collections.Generic;

namespace lecture
{
    class MainClass
    {

        public static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            long[] P = new long[100];

            P[0] = 1;
            P[1] = 1;
            for (int i = 2; i <= N; i++)
            {
                P[i] = P[i - 1] + P[i - 2];
            }

            Console.WriteLine(P[N]);
        }
    }
}