using System;

public class Program

{

    public static void Main()

    {

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

        var f0 =1;

        var f1 = 1;

        var res = 0;

        if ( n < 2) {res = 1;}

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

        { 

            res = f0 + f1;

            f0 = f1;

            f1=res;

        }

        Console.WriteLine(res);

    }

}