using System;
using System.Collections.Generic;

namespace lecture
{
    class MainClass
    {

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

            long[] A = new long[N+1];

            A[0] = 1;
            A[1] = 1;

            for (int i = 2; i < N+1; i++)
            {
                A[i] = A[i - 1] + A[i - 2];
            }
            Console.WriteLine(A[N]);
        }
    }
}