using System;

public class Program

{

    public static void Main()

    {

        int n = Convert.ToInt32(Console.ReadLine());

        int i = 1;

        int sec = 0;

        int last = 1;

        int[] toSum = new int[n];

        toSum[0] = sec;

        toSum[1] = 1;

        while (i <= (n-2))

        {

            int newNumber = sec + last;

            sec = last;

            last = newNumber;

            i++;

            toSum[i] = last;

        }

        Console.WriteLine(toSum[n-1]);

    }

}