using System;

public class Program

{

    public static void Main()

    {

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

        int num0 = 1;

        int num1 = 1;

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

        {

            int numNext = num0 + num1;

            num0 = num1;

            num1 = numNext;

        }

        Console.WriteLine(num1);

    }

}