using System;

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

            long[] dp = new long[N];
            dp[N - 1] = 1;
            dp[N - 2] = 2;
            for(int n = N-3; n >= 0; n--)
            {
                dp[n] = dp[n + 1] + dp[n + 2];
            }
            Console.WriteLine(dp[0]);
        }
    }
}