using System;
using System.Collections.Generic;
using System.IO;

class CalcFib {

    static void Main(String[] args)
    {
        // Set n equal to an integer taken from user input
        int n = Convert.ToInt32(Console.ReadLine());

        // Output the calulated fib number
        Console.WriteLine(Fibonacci(n));
    }

    public static int Fibonacci(int n)
    {
        // Declare integer variables to be used in the fibonacci sequence
        int a = 0, b = 1, c = 0;

        // To return the first Fibonacci number
        if (n == 0) return a;

        // Run a for loop to calulate all fibonacci numbers after 0
        for (int i = 2; i <= n; i++)
        {
            // New fib number is equal to sum of past 2 numbers
            c = a + b;
            a = b;
            b = c;
        }

        // Return the calculated fib number
        return b;
    }
}