using System;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Gauss: " + GaussianFormula(5));

        Console.WriteLine("Fibonacci Regular: " + Fibonacci(100));

        Console.WriteLine("Fibonacci Fast: " + FastFibonacci(100));

    }

​

    public static int GaussianFormula(int k)

    {

        return (int)Math.Round((double)((k * (k + 1)) / 2));

    }

​

    public static double Fibonacci(int n)

    {

        if (n <= 0)

        {

            return 0;

        }

​

        double pastNum = 0;

        double currentNum = 1;

        for (int i = 1; i < n; i++)

        {

            var temp = pastNum + currentNum;

            pastNum = currentNum;

            currentNum = temp;

        }

​

        return currentNum;

    }

​

    //Check that these are named correctly...

    //Use these. Not the gets

    //public static double GoldenMean => ((1+Math.Sqrt(5))/2);

    //public static double GoldenNumber => ((1-Math.Sqrt(5))/2);

    public static double GoldenMean

    {

        get

        {

            return ((1 + Math.Sqrt(5)) / 2);

        }

    }

​

    public static double GoldenNumber

    {

        get

        {

            return ((1 - Math.Sqrt(5)) / 2);

        }

    }

​

    public static double FastFibonacci(int n)

    {

        return ((Math.Pow(GoldenMean, n) - Math.Pow(GoldenNumber, n)) / Math.Sqrt(5));

    }

}