using System;

public class Program

{

    public static void Main()

    {     

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

var f0 = 1;

var f1 = 1;

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

{

var fNext = f0 + f1;

f0 = f1;

f1 = fNext;

}

Console.WriteLine(f1);

        }

    }

​