using System;

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