using System;

public class Program

{

    public static void Main()

    {

       var n = int.Parse(Console.ReadLine());

        var f0 = 1;

        var f1 = 1;

        for(var i=0;i<n-1; i++)

        {

            var fNext  = f0+f1;

            f0 =f1;

            f1 = fNext;}

        Console.WriteLine (f1);

    }

}