using System;
using System.Linq;
using System.Collections.Generic;
class Program
{
    static void Main(string[] args)
    {
    	long N = long.Parse(Console.ReadLine());
    	var array = new long[N + 1];
    	
    	array[0] = 1;
    	array[1] = 1;
    		
    	for(long i = 2;i < N + 1;i++)
    	{
    		array[i] = array[i - 1] + array[i - 2];
    	}
    	Console.WriteLine(array[N]);
    }
}