FibonacciNumbers

using System;

namespace Fibonacci_Numbers
{
    class StartUp
    {
        static void Main()
        {
            int fibonacciNumber = int.Parse(Console.ReadLine());
            Console.WriteLine(FibonacciNumber(fibonacciNumber));
        }
        private static int FibonacciNumber(int fibonacciNumber)
        {
            int firstNumber = 0;
            int secondNumber = 1;
            int nNumber = 0;
            if (fibonacciNumber == 0 || fibonacciNumber == 1)
            {
                return fibonacciNumber = 1;
            }
            else
            {
                for (int i = 0; i < fibonacciNumber; i++)
                {
                    nNumber = firstNumber + secondNumber;
                    firstNumber = secondNumber;
                    secondNumber = nNumber;
                }
                return nNumber;
            }
        }
    }
}