using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Problem_1.Reverse_Numbers_with_a_Stack
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            var stack = new Stack<long>();

            stack.Push(1);
            stack.Push(1);

            for (int i = 0; i <n-1; i++)
            {
                if (stack.Count==n)
                {
                    break;
                }
                long fibOne = stack.Pop();
                long fibTwo = stack.Peek();
                stack.Push(fibOne);
                stack.Push(fibOne + fibTwo);
            }
                Console.WriteLine(stack.Pop());
        }
    }
}