using System;

​

public class Program

{

    public static void Main()

    {

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

        long sum = Fib(number);

        Console.WriteLine(sum);

    }

​

    public static long Fib(int n)

    {

        if (n <= 2)

        {

            return 1;

        }

​

        return Fib(n - 1) + Fib(n - 2);

    }

}