using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        // Give the nth Fibonacci number

        // Starting with 0, 1, 1, 2, ... 

        // a Fibonacci number is the sum of the previous two.

​

        Console.WriteLine(Fibonacci(0));

        Console.WriteLine(Fibonacci(1));

        Console.WriteLine(Fibonacci(2));

        Console.WriteLine(Fibonacci(3));

        Console.WriteLine(Fibonacci(20));

    }

​

    public static int Fibonacci(int n)

    {

        List<int> sequence = new List<int>()

        {

        0, 1

        }

​

        ;

        int value_at_place = 0;

        if (n < 0)

        {

            value_at_place = 0;

        }

        else

        {

            switch (n)

            {

                case 0:

                case 1:

                    value_at_place = sequence[n];

                    break;

                default:

                    for (int i = 2; i <= n; i += 1)

                    {

                        sequence.Add(sequence[i - 1] + sequence[i - 2]);

                    }

​

                    value_at_place = sequence[n];

                    break;

            }

        }

​

        return value_at_place;

    }

}